Soviet President Yuri Andropov offered tonight to "liquidate" all the missiles that the Soviet Union would pull out of Europe as part of an agreement on limiting medium-range nuclear weapons in Europe, including "a considerable number" of modern SS20s.

He made his offer contingent on a U.S. agreement not to deploy any of the Pershing II and cruise missiles now scheduled to be deployed in Western Europe before the end of the year.

Previously Moscow had said it would move a number of its intermediate-range missiles east of the Ural Mountains if the United States would agree not to deploy its new missiles in Europe.

The offer appeared to respond to U.S. and Western European insistence that a mere removal of Soviet SS20 missiles behind the Ural Mountains would not be an acceptable way of curbing medium-range arms in Europe.

Speaking to a correspondent for the Communist Party newspaper Pravda, Andropov renewed his demand that the United States abandon its planned deployment of 572 Pershing II and cruise missiles in five Western European nations. He renewed Moscow's offer to cut its medium-range missile force to 162, the same number Britain and France have. The United States and NATO maintain that the British and French missiles are part of those countries' independent nuclear deterrent forces and should not be counted in any U.S.-Soviet agreement.

In Washington, the State Department said the Soviet offer to destroy its missiles would be "a positive sign" if presented officially at the Geneva arms control talks. The statement added, however, that Andropov's remarks showed no change in the Soviet effort to include the number of British and French missiles in the arms control calculations, which is unacceptable to the United States and its NATO allies.

The State Department also objected that the Soviets "continue to seek an agreement that would be limited only to Europe," allowing the Soviets to continue to increase the number of missiles they deploy in other parts of the world.

Speaking to reporters while leaving a political meeting in Santa Barbara, Calif., Reagan said he had not seen Andropov's offer, Washington Post staff writer David Hoffman reported. Asked what he thought about the offer to reduce the number of Soviet missiles, the president said, "That's what we're trying to get them to do."

In the interview, Andropov continued, "We are ready to make another major step.

"Should a mutually acceptable agreement be achieved, including renunciation by the United States of the deployment of new missiles, the Soviet Union, in reducing its medium-range missiles in the European part of the country to the level equal to the numbers of missiles of Britain and France, would liquidate all the missiles to be reduced," he said. "In this event a considerable number of the most modern missiles, known in the West as SS20s, would be liquidated as well."

According to western estimates, Moscow has 351 triple-warhead SS20 missiles deployed as part of its medium-range forces. Of this number, 251 are believed to be stationed in the European part of the Soviet Union and the rest are situated in the Asian part of the country, presum- ably targeted on Japan and China.

Andropov's proposal to dismantle "all the missiles to be reduced" under an agreement with the United States was the first such specific Kremlin statement since the two countries began talks in Geneva in 1981 on reducing the number of medium-range nuclear weapons in Europe. Previously the Soviets have indicated that some medium-range nuclear weapons could be dismantled while others would be moved into Siberia out of range of Western Europe.

Some Western Europeans have argued that the mere removal to Siberia of the mobile SS20 missiles would not fundamentally change their security problems since these weapons could be redeployed quickly in the European part of the Soviet Union.

Japan and China have objected strongly to the removal of these weapons to the Asian part of the Soviet Union on the ground that they would constitute an additional threat to their security.

Andropov said his offer was a gesture of good will all around. Addressing Western Europe, he said it rendered "totally groundless" assertions in NATO circles that Moscow intended to retain "the SS20 missiles which are to be reduced." He said Japan and China should have no concerns that the missiles would be relocated closer to their territories.

Addressing Washington, Andropov said his offer "makes it clear to any unprejudiced person that the Soviet Union has done and is doing everything in its power to find solutions" at Geneva and that it wants to achieve an agreement with the United States to "prevent a new and extremely dangerous round in the nuclear arms race in Europe."

The Pravda interview, which was distributed by the government news agency Tass, quoted Andropov as saying that the Soviet Union and NATO should reduce by two-thirds their existing medium-range nuclear weapons in Europe, "retaining for the time being 300 such systems."

The 300 figure would include 162 medium-range missiles, or the level of the combined total of France and Britain, on each side, the rest being medium-range nuclear aircraft. Andropov said Moscow was prepared to reach agreement on equal numbers of warheads or nuclear charges carried by the missiles and aircraft.

While the tone of his remarks was moderate, Andropov reaffirmed Moscow's intention to take "countermeasures" should the United States proceed with the deployment due to start at the end of this year. Moscow has indicated that it would introduce nuclear weapons in East Germany and possibly Czechoslovakia.

He said the the offer to dismantle new Soviet rockets along with the old SS4 and SS5 missiles was an indication of the Kremlin's flexibility. But, he added, "our flexibility has its limits, which are dictated by the security interests of the Soviet state and its allies."

Western obervers here said that the Soviet offer may have been resented by the armed forces chiefs and that they may not be happy about the prospects of "liquidation" of their modern SS20s. Andropov was apparently able to prevail over their objections.

Apart from the arms control issue, Andropov also chose to address the leaders of China. He noted "some positive tendencies" in relations between China and the Soviet Union.

But, Andropov said, these relations are "far from being" what they should be "between such big and, moreover, neighboring powers." He renewed Soviet proposals for expanding trade and other exchanges and proposed unspecified confidence-building measures to ease tensions along the Sino-Soviet border.

Well-informed sources said earlier that Soviet Deputy Foreign Minister Mikhail Kaptisa was prepared to discuss concrete proposals for a pullback of military forces now stationed along the border when he pays an official visit to Peking in early September.

Apparently having in mind Kaptisa's visit and the opening of the third round of Sino-Soviet political talks in early October, Andropov tonight asserted that Moscow was prepared "for a political dialogue with China on fundamental questions" of international relations including "international security problems."