Defense Secretary William J. Perry, with his Russian and Ukrainian counterparts, planted sunflowers on a former Soviet missile silo today to mark Ukraine's complete nuclear disarmament.

At the Pervomaysk missile base in southern Ukraine, the officials planted the flowers in a plowed field of black earth atop the destroyed remains of missile Silo 110. During the Cold War, the base, amid flat Ukrainian farmlands that resemble the American Midwest, held more than 80 such silos, with 700 nuclear warheads aimed at the United States.

The ceremony celebrated Ukraine's abandonment of the world's third-largest nuclear arsenal, which it inherited in the 1991 collapse of the Soviet Union. It also marked the near completion of a primary U.S. strategic goal since the Soviet breakup: to gather all ex-Soviet nuclear weapons in Russia, thus avoiding a proliferation of nuclear powers.

Ukraine announced Saturday that it had transferred the last of 4,400 nuclear warheads to Russia, joining Kazakhstan, another former Soviet republic, as the only countries ever to have given up nuclear arms with verification. Belarus, the other country that inherited Soviet nuclear weapons, is expected to transfer its last 18 warheads to Russia by the end of the year.

Perry, with Ukrainian Defense Minister Valeriy Shmarov and Russia's Gen. Pavel Grachev, spaded soil, planted young sunflowers and watered them with metal watering cans in the ceremony, shown on Ukrainian television tonight. The three nations' roles in disarming Ukraine "are ensuring that our children and our grandchildren will live in peace," Perry said.

Following the breakup of the Soviet Union, Ukraine lacked money to maintain and use nuclear weapons. But in a country with a devastated economy, a domineering neighbor in Russia and little call on global attention, some Ukrainians favored keeping nuclear missiles as a source of influence. Still, after long negotiations, Ukraine signed a deal in 1994 with Russia and the United States giving up the warheads in exchange for $1 billion in aid, mostly in the form of Russian uranium fuel for its nuclear power stations.

Ukraine's denuclearization "is globally significant" in countering nuclear proliferation, said Fred Ikle, an arms control specialist who served as undersecretary of defense in the Reagan administration. "The Ukrainians recognized that having a pile of nuclear weapons did not make them safer . . . {and} is not an essential aspect of being an important country," Ikle said in a telephone interview.

Ukrainian President Leonid Kuchma said Saturday that "the Ukrainian people, having suffered from the Chernobyl nuclear accident, are well acquainted with the potential disaster that nuclear weapons can bring. Ukraine calls on other nations to follow our path and to do everything to wipe nuclear weapons from the face of the earth as soon as possible." Kuchma repeated a Ukrainian call for a nuclear-free zone in Eastern Europe to reduce tensions that have risen in the last three years between NATO and Russia over NATO's plans to expand.

Ukraine has voiced fears that, having given up its warheads, it risks being shortchanged on the aid promised in return. Kuchma's top security adviser, Volodymyr Horbulin, complained in April that Russia had not "provided Ukraine with even a single nuclear fuel rod this year." And Congress has tried to cut funds promised to Ukraine by the Clinton administration to help build housing for missile troops forced out of their jobs.

Today, Perry underscored the administration's commitment to continue aid to Ukraine by signing over another $43 million to help dismantle silos and build housing at the former Soviet missile bases at Pervomaysk and Khmelnytskyy. Perry has personally monitored the disarmament of Pervomaysk, visiting four times in the past two years in what U.S. officials said is partly an effort to highlight Ukraine's cooperation on security issues and to maintain support for aid in Congress. The only former Soviet nuclear missiles still outside Russian borders are 18 SS19 missiles in northwestern Belarus. CAPTION: Ukrainian Defense Minister Shmarov, left, and his U.S. counterpart Perry water sunflowers.