BRUSSELS, Belgium--President Bush said yesterday it's too early to proclaim an end to the Cold War, but added that Mikhail S. Gorbachev's acceptance of sweeping reform in Eastern Europe "absolutely mandates new thinking" by the West.

Wrapping up his weekend summit journey with a stop at NATO Headquarters, Bush also told reporters the United States would maintain "significant military forces in Europe as long as our allies desire our presence."

The president said he wants a treaty making initial cuts in the superpowers' conventional forces in Europe "in the bank" before seeking deeper reductions. He told NATO leaders he hoped a multinational summit could be convened in Europe next summer to sign such an accord.

Conventional forces aside, the United States and Soviet Union are negotiating a proposed 50 percent cut in long-range nuclear weapons, as well as a proposed ban of chemical weapons.

The president spoke as Gorbachev was convening a meeting of a radically reordered Warsaw Pact in Moscow to review the weekend summit.

The dramatic change in Europe continued uninterrupted during the day, as the Soviet Union and the four other Warsaw Pact nations condemned their own invasion of Czechoslovakia in 1968. In Leipzig, East Germany, about 200,000 demonstrators broke into wild rounds of applause as speakers called for German reunification.

Bush and Gorbachev leaders agreed at an unprecedented joint news conference before leaving Malta that their meeting heralded a new era of cooperation in East-West relations, including arms control and trade. They intend to meet again in the United States in the second half of June.

At his news conference, Bush said, "We stand at the threshold of a new era..." but declined to assert the Cold War has ended as Gorbachev suggested.

"That day hasn't arrived," the president said when asked about Gorbachev's statement declaring an end to the "epoch of the Cold War."

Barring a utopian development, Bush said, "theUnited States must stay involved" by keepingtroops massed against Warsaw Pact forces.

"If you want to project out 100 years, or takesome years off of that, you can look to a utopianday when there might be none [U.S. troops inEurope]," he said. "But as I pointed out to them[NATO leaders], that day hasn't arrived--and theyagree with me."

Dutch Prime Minister Ruud Lubbers said he wasimpressed by the United States' "extraordinarilypositive attitude" toward events in Europe.

"It has nothing to do with a 'we are pullingout' attitude," he told reporters. "On thecontrary, they are again promising a meaningfulpresence [in Europe]."

British Prime Minister Margaret Thatcher saidBush's speech "was so full of meat that we reallyshould consider it very carefully before we replyto it." She has urged a more cautious attitudethan some allies toward events unfolding inEastern Europe.

The president began his news conference with astatement that said a "peaceful revolution" wastaking place in Eastern Europe, where fivehardline communist regimes have fallen in recentweeks.

He said his goal was to see "individual freedomeverywhere replace coercion and tyranny."

Bush, apparently referring to disagreementsabout Central America, said "all was not sweetnessand light" at the Malta summit, but took pains toapplaud Gorbachev's handling of the change inEastern Europe.

"As I watched the way in which Mr. Gorbachevhas handled the changes in Eastern Europe, itdeserves new thinking. It absolutely mandates newthinking," he said.

Asked what had emerged at the summit, he said"I think he took my measure and I took his and Ithink we both feel more comfortable about ourcommon objectives.