Former Soviet Foreign Minister Eduard A. Shevardnadze appealed to the United States on Monday for financial aid to help prevent a Soviet return to the past that "would be a catastrophe."

President Bush said last week that Moscow's request for an additional $1.5 billion in credit guarantees to help buy food is "up in the air" and may depend on Soviet efforts to improve their credit worthiness and food-distribution system.Shevardnadze, launching his first speaking tour since abruptly quitting President Mikhail S. Gorbachev's government 41/2 months ago, said restructuring the Soviet Union is essentially a Soviet problem that will require many years to achieve.

"But it's also clear that we cannot avoid getting assistance from the outside," he said. "Not necessarily charitable assistance but rather technological, intellectual and financial assistance on very favorable terms."

Shevardnadze said the danger of dictatorship that he warned about when he resigned has abated somewhat. And he expressed a measure of optimism that a recent pact between the leaders of nine Soviet republics may help avert chaos or civil war.

In an address to the Brookings Institution before traveling to the State Department and White House for meetings with Secretary of State James A. Baker III and President Bush, Shevardnadze outlined his vision of a "new world order," which Bush also speaks of often.

Shevardnadze proposed international sanctions to compel Arab and Israeli negotiators to join peace talks Baker is trying to arrange, and he called for an end to supplying weapons to opposing sides in the Middle East.

Reflecting on the progress made in East-West relations during his tenure as Soviet foreign minister, Shevardnadze said, "Not only has the Cold War come to an end, the era of . . . great ideological opposition has come to an end."