MOSCOW, SEPT. 12 -- Soviet Foreign Minister Eduard Shevardnadze leaves here Sunday for three days of talks in Washington, with Soviet officials hinting that he will take a rigid stance in the final phase of negotiations for a treaty to scrap intermediate-range missiles.

A senior member of Shevardnadze's delegation signaled this weekend that differences between the United States and the Soviet Union over West German-based Pershing IA missiles that are blocking the proposed nuclear arms accord will carry over into the talks in Washington, scheduled to begin Tuesday.

Soviet arms control specialist Viktor Karpov indicated that the U.S. position that West Germany's Pershings should not be included in the proposed bilateral accord would make it unlikely that the Soviets would agree to eliminate shorter-range missiles in the 300- to 600-mile range, such as the Pershings. The missiles are owned by West Germany, but their nuclear warheads are controlled by the United States. The accord would also cover intermediate-range missiles of between 600 and 3,500 miles.

"If the United States wants to take the missiles out of an accord, this amounts to an attempt to destroy the very idea" of the proposal to dismantle the shorter-range missiles, Karpov said in an interview released by the Soviet news agency Tass yesterday.

The Soviet side is also braced to rebut a Reagan administration objection to having destruction of the warheads included in a U.S.-Soviet treaty, according to a Tass analysis released here today.

After reporting the arguments that U.S. Secretary of State George P. Shultz gave in explaining the U.S. objection to destroying the warheads, Tass asked, "Isn't this proof that the U.S. leadership has abruptly recoiled from the emerging accord under the influence of American quarters that want no agreements with the Soviet Union?"

Despite the Soviets' pessimistic tone toward the coming talks, however, the overriding Soviet interest is in nailing down the terms of an accord and setting the dates of a third meeting between Kremlin leader Mikhail Gorbachev and President Reagan, western diplomats in Moscow said.

The coming celebration ceremonies for the 70th anniversary of the Soviet Union underline the need for Gorbachev to achieve a concrete success in foreign policy, the diplomats said.

Against that background, the last-minute objections raised publicly here may be a smoke screen for new Soviet arms proposals or a Soviet desire to wrap up the final details of the accord under negotiation.

"I often find that Soviet rhetoric becomes most hard-line when they feel they can clinch an agreement," a senior American diplomat said here.

One indication that Shevardnadze plans to use the talks for fine-tuning agreements already well under way is that his accompanying delegation consists of only a few assistants, all of whom have been actively involved in the preparatory talks for the meeting.

In addition to Karpov, who is head of the Foreign Ministry's disarmament agency, Shevardnadze's entourage will include Deputy Foreign Minister Alexander Bessmertnykh, Soviet Ambassador to the United States Yuli Dubinin, arms negotiator Alexei Obukhov, Shevardnadze's aide A. Tarasenko and Foreign Ministry press spokesman Gennadi Gerasimov. Only Tarasenko and Bessmertnykh specialize in American affairs.

Soviet officials have said that the talks, scheduled for Tuesday to Thursday, are primarily designed to discuss arms control issues relating to the treaty.

In a briefing here this weekend, however, a U.S. official said the proposed treaty would by no means dominate discussion. Shultz will want to discuss Soviet human rights violations as well as arms control, and the eight-year-old Soviet military intervention in Afghanistan is likely to be another major agenda item, the official said.

Preparations for the meetings, which will include talks between Shevardnadze and Reagan as well as major sessions with Shultz, are regarded by western diplomats here as the most thorough of any during the Reagan administration.

Preparatory meetings have been held during the past month in Moscow, Geneva, Vienna, Bern, Switzerland, and other West European cities. Arms negotiators in Geneva have delayed a scheduled break in order to complete the details of an accord.

For Shevardnadze, 58, a novice in foreign affairs when he became foreign minister two years ago, the meetings are considered to be a major test.

Already, the Soviet leadership has begun to counter its hard-line stance on the proposed arms treaty with a few scattered signs of good will. For example, the Soviet weekly Ogonyok today published a full interview with the American ambassador here, Jack Matlock, the first such treatment of a U.S. envoy in the official Soviet media in memory.

Soviet officials have received American visitors recently at the Soviet radar station at Krasnoyarsk and Soviet military facilities in Minsk. These visits are seen as signs of Moscow's flexibility on the issue of verification, a potential obstacle in the talks.

In an apparent attempt to stem criticism from Shultz on human rights, Moscow also this week granted Soviet Jewish activist Josef Begun and several other dissidents permission to leave the Soviet Union.

Following the meetings in Washington, Shevardnadze is expected to spend a week at the United Nations in New York and then travel to South America on Sept. 27.