KIEV, Ukraine— The Ukrainian Defense Ministry began like a revolutionary cell, with three officers. In the months after Ukraine's declaration of independence on Aug. 24, 1991, President Leonid M. Kravchuk and the present Defense Minister, Gen. Konstantin Morozov, began a series of quiet visits to Soviet military bases.

A sovereign Ukraine would emerge from the collapsing empire, they told senior officers, and an independent army would be central to the new state. Anyone willing to take an oath of allegiance to Ukraine would be guaranteed his job and full pension and other rights, including citizenship.

These visits increased as the Soviet Government disintegrated, and by the end of January 350,000 servicemen and a large majority of officers in the three Ukrainian military districts had taken the oath.

By the time the Russian President, Boris N. Yeltsin, and the Commander in Chief of the Commonweath of Independent States' armed forces, Marshal Yevgeny I. Shaposhnikov, could pay much attention, an important part of the Soviet military had been pulled out from underneath them. A Message for Moscow

While the leaders of other non-Baltic states seemed to dither, Ukraine's prickly and intense commitment to sovereignty and independence had never been more obvious, or effective.

Ukraine, the second most populous former Soviet republic after Russia, has considerable economic and political problems at home. But the new state continues to define what sovereignty means to the rest of the artificial commonwealth, and it is trying to insure that Russia, however reluctantly, gets used to the idea. And with nearly the population of France, a sizable army and considerable natural resources, Ukraine will be a significant regional and European power.

The commonwealth was created with Ukraine in mind, since Kiev insisted it would not join any structure that called itself a state or contained any "center," as St. Petersburg and Moscow had been for the Russian and Soviet empires. The commonwealth would be an association of equal and equally independent states, Mr. Kravchuk insisted, or it would be nothing.

This has been the basis of Ukraine's policy of "active independence," said Yuri A. Sergeyev, the Foreign Ministry spokesman. "We reject any Russian desire to retain a single unified political, military, economic or financial space," he said. Many Areas of Conflict

But in Kiev's struggles with Moscow over the Black Sea Fleet, now to be run jointly, somehow, until the end of 1995, and over Crimea, ceded to Ukraine in 1954 and now granted a form of autonomy, there are many areas for misunderstanding and conflict.

There are also disputes over Ukraine's intention to abandon the ruble and create its own currency, over the extremely slow transfer of bank payments between Russian and Ukrainian enterprises, and even over the prices to be paid for what has suddenly become international trade.

Mr. Yeltsin and Mr. Kravchuk have worked hard to defuse these problems, but each is struggling with more hot-headed nationalists. No Ukrainian forgets that within two days of Ukraine's independence declaration, a Yeltsin spokesman said Russia reserved the right to review its borders with all states of the former union except the Baltics, despite a Ukrainian-Russian treaty signed the previous November guaranteeing territorial integrity.

Mr. Yeltsin's Vice President, Aleksandr V. Rutskoi, regularly insists Russia has the right to defend Russian-speakers outside its borders, a discomfiting thought here, where there are at least 7 million and perhaps 11 million ethnic Russians out of a total multi-ethnic population of some 53 million.

Russian troops have been engaged in fighting in Moldova, in support of a separatist enclave, even though Moldova does not border Russia at all, but Ukraine. And most Russian officials, if pressed, say they believe that Ukraine and Belarus will both come back, one day, into Moscow's embrace.

Ukrainian nationalists, for their part, become outraged over reports of discrimination against Ukrainian sailors of the Black Sea Fleet, and they tend to see the meddling hand of Russia behind every problem.

"Russia simply can't put up with the idea that we're an independent state," said Maj. Aleksandr M. Kluban, the Defense Ministry spokesman. "They do it formally. We recognize them as a great power, but they still don't treat us as an independent, sovereign state."

But Ukraine, whose new Foreign Ministry has at least some diplomats with United Nations experience, has made great progress in carving out a coherent foreign and military policy.

Eight months ago, Ukraine's stance seemed to frighten the West, nostalgic for an orderly union and a single command over nuclear weapons. But Mr. Kravchuk has promised that Ukraine will be a neutral and nonnuclear state, has signed all appropriate international treaties, and handed over Ukraine's several thousand short-range nuclear weapons to Russia by May 7, two months earlier than scheduled.

While Mr. Kravchuk insists Ukraine keep "administrative control" over its 176 long-range nuclear missiles, so far the term is only rhetorical, Ukrainian officials and Western diplomats say. Ukraine cannot fire those weapons on its own, and real control over them is retained, as agreed, by the central commonwealth nuclear command.

Under the Strategic Arms Reduction Treaty, Ukraine must eliminate 130 of these 176 weapons in the next seven years, but Mr. Kravchuk has promised to get rid of them all by the end of 1994.

A request by Ukraine in May that Washington give it a security guarantee was rebuffed by Secretary of State James A. Baker 3d. Mr. Baker told Mr. Kravchuk that Ukraine's best security guarantee was to act like a sovereign state and become quickly immersed in international organizations and treaties.

Ukraine has taken that advice, sending 420 soldiers on a difficult United Nations peacekeeping mission near Sarajevo, where several Ukrainians have already been wounded or killed. "They risk their lives," Major Kluban said. "But it's for the dignity of the state."

Ukraine wants to join the European Community, but given Turkey's experience, that is not likely to happen soon. Negotiations are planned or under way to enter the Council of Europe and the European Parliament, and Ukraine will sign existing conventions on human rights, consular affairs and so on. Ukraine also sees some protection in Western investment, and has passed a liberal foreign-investment law.

Some Ukrainian legislators, like Mykhailo M. Horyn, leader of the Ukrainian Republican Party, say they may oppose ratifying the Strategic Arms Reduction Treaty and the Nuclear Nonproliferation Treaty when Parliament returns this fall, because Russia continues to make threatening noises over Crimea and the Black Sea Fleet and is accused of stirring up Russian nationalism around Donetsk and Donbass. Ratification Is Expected

"No state guarantees us security," Mr. Horyn said. Speaking of Ukraine's transfer of nuclear weapons to Russia, he said, "The biggest nuclear state in Europe is disarming, and taking its nuclear weapons to a neighboring state that says it may reconsider our borders."

But Western diplomats agree with First Deputy Prime Minister Valentin K. Simonenko that the treaties will be ratified anyway, if only because Mr. Kravchuk's own credibility, let alone that of the new state, depends on it.

Mr. Sergeyev, the Foreign Ministry spokesman, said the military was drafting a new doctrine to fulfill its tasks as a regional, not a strategic power.

Military officials say the army will be smaller and, in time, all-volunteer. There were 800,000 to a million troops on Ukrainian territory; Major Kluban would not say how many have taken the oath to Ukraine. By 1994, the armed forces will be reduced to about 420,000. By 1998, they should be halved again, he said, to between 220,000 and 260,000, which is all Ukraine needs or wants.

A sense of the larger problem with Russia can best be seen in the negotiations over the 300 or so ships of the Black Sea Fleet.

Mr. Yeltsin and Mr. Kravchuk finally agreed to negotiate to split the fleet, and Moscow suggested 40 percent for Ukraine. The percentages were less of a problem for Kiev, since some ships are outdated or useless to Ukraine, than was the definition of how percentages would be applied.

Russia insisted, Major Kluban said, on dividing up everything, including the entire coastal infrastructure, while keeping the main base of Sevastopol. But Ukraine rejected the idea as an infringement of sovereignty. Instead, Kiev offered to rent Russia what it needed, including Sevastopol, until Moscow could build its own Black Sea base.

But Mr. Yeltsin has his own nationalists. The flight in July of a small coast guard ship from Crimea to Odessa, because the Ukrainian officers claimed discrimination against them, threatened a larger conflict.

At their summit meeting on Aug. 3, however, Mr. Yeltsin and Mr. Kravchuk found a better way out, which was to postpone the whole messy business until the end of 1995 and put the fleet under their joint personal control until then, with new symbols and flags.

What those would look like, or how two military commands would share telephones and patrols, was left to "experts" to decide. The Ukrainian Defense Ministry's first reaction was shock. But it was another example of Mr. Kravchuk's skill at preserving the symbols of Ukrainian sovereignty, while understanding that Moscow and Kiev are condemned to get along if either government is to survive.

Photo: President Leonid M. Kravchuk of Ukraine, who has promised that his country will be a neutral and nonnuclear state. (Efrem Lukatsky for The New York Times) Map of Ukraine highlighting Kiev