The Soviet Union confirmed today that it has proposed at the Geneva arms talks that Britain and France freeze their nuclear arsenals while the Soviets and Americans destroy their European-based missiles.

Soviet Deputy Foreign Minister Georgi Kornienko clarified the Kremlin position on the British and French missiles during a press conference at which he and two other senior officials expanded on Soviet leader Mikhail Gorbachev's long-term plan for worldwide nuclear disarmament announced Wednesday. The briefing also aimed to combat U.S. objections to various aspects of the proposal.

Both the French and the British have objected in the past to consistent Soviet calls to include their nuclear forces in the U.S.-Soviet talks at Geneva. An offer to accept a freeze on British and French missiles appears to be a concession to the western view on medium-range missiles in the European theater.

Both France and Britain have announced plans to modernize their submarine-based forces by the end of the century. In a speech to French legislators during a trip to Paris last October, Gorbachev called for the first time on France and Britain to join Moscow in direct arms talks.

Government spokesman Leonid Zamyatin said that along with the positive responses to Gorbachev's announcement, Defense Secretary Caspar W. Weinberger and other U.S. officials have posed "some problems," such as continued support of the Strategic Defense Initiative, opposed by the Soviet Union, and opposition to the nuclear test ban, which Moscow backs.

Sergei Akhromeyev, chief of the Soviet general staff, stressed that if the Gorbachev plan is approved, the Europe-based medium-range missiles on both sides would be "destroyed," and the destruction will be verifiable by international means. Kornienko countered arguments that Soviet SS20 missiles based in Asia could be shifted easily to the European theater by saying that U.S. Pershing IIs could be moved to Western Europe more quickly.

All three Soviet officials seemed eager to strike a tone of compromise about the Gorbachev proposal.

"If there have been issues of verification," Kornienko said, "we have no verification problems, and we are prepared to go as far here as will be needed."

Asked whether failure to achieve at least partial agreement with Washington on the plan would mean an unsuccessful second summit between President Reagan and Gorbachev, Kornienko said, "Let's be optimistic, and let's seek a constructive dialogue and not ask hypothetical questions."

Holding up a glass with water in it, he said, "Let's call this half full."

Kornienko indicated that the Gorbachev proposal "is the focus of our attention for the summit meeting." At the November summit, Gorbachev and Reagan agreed to meet again this year. Several alternative dates have been put forward, one of the Soviet officials said, but no decision has been made.

Spokesman Zamyatin stressed that the bilateral disarmament on intermediate-range missiles would be contingent on a U.S.-Soviet "ban on the development, testing and deployment of space-strike arms." Falling in the first stage of Gorbachev's 15-year plan for worldwide nuclear disarmament, it would take place during the next five to eight years.

In that period, Britain and France "should not build up their respective weapons," Kornienko told journalists at the rare Saturday press conference.

During the next stage, the two countries could determine whether they would follow suit and eliminate their nuclear arsenals, Kornienko said.

He added that Soviet delegates in Geneva already have put forward the arms control aspects of the Gorbachev plan and that other parts of it would be offered by Soviet negotiators at talks in Vienna and Stockholm.

The new Soviet proposal on medium-range weapons represents a major departure from the longstanding Soviet position linking reductions of Soviet European-based SS20s with concurrent reductions of U.S. intermediate-range missiles in Europe, together with reductions of British and French weapons.

Kornienko distinguished the Soviet proposal from the U.S.-proposed "zero option," favored by the Reagan administration. The zero option called for eliminating nuclear weapons in Asia, and it did not preclude the movement of U.S. missiles to Europe, Kornienko said. "We have not proposed anything of the kind," he added.

With respect to the Reagan administration's SDI program -- popularly known as "Star Wars" -- to develop a space-based missile defense, Akhromeyev said that basic verifiable research would be permitted under the Soviet proposal as long as it did not lead specifically to the design of space-strike weapons.

"We are not talking about banning basic research," he said, but only "what goes beyond basic research and becomes goal-oriented or directed research specifically designed to develop a weapons system."

Akhromeyev also elaborated on Gorbachev's proposal for verifying the U.S.-Soviet troop reductions under the Vienna talks, saying that "apart from national technical means of control, we envisage also such measures as an exchange of the lists of the reduced military units, mutual notification about the start and completion of reduction, and creation by each side, for the period of withdrawal, of three or four points of observation for the withdrawal of reduced troops."