Soviet Foreign Minister Eduard Shevardnadze will come to the United States later this month with specific details on the arms-control proposals mentioned recently by Soviet leader Mikhail Gorbachev, according to Soviet sources.

Shevardnadze is scheduled to meet with President Reagan on Sept. 27 in Washington and with Secretary of State George P. Shultz both before and after that session.

The Soviet foreign minister, according to these sources, will expand on Gorbachev's allusion to "radical proposals" for nuclear-arms reductions in a session with U.S. senators in Moscow on Sept. 3. He will also present Soviet ideas on restraining research on strategic defenses against nuclear missiles, frequently referred to as Star Wars and described by Moscow as "space strike weapons."

Asked whether the United States has been told of a forthcoming proposal to be brought by the Soviet foreign minister, White House national security affairs adviser Robert C. McFarlane said yesterday:

"We have no basis for expecting anything new. However, we would be very pleased were they to make a new proposal and we would welcome it."

Although one White House official initially dismissed the prospect of a significant Soviet proposal as a "canard," a more senior administration official later said, "We would welcome a concrete proposal by the Soviet Union which would result in deep reductions in offensive arms in a manner which enhances stability. The Soviet position in the Geneva talks thus far has been vague, one-sided and filled with preconditions."

The Soviet sources would provide no details on what Shevardnadze will deliver, but emphasized that if the proposals draw "interest" from the United States, they then will be presented by the Soviet delegation in Geneva, where arms control talks will resume this week.

Ever since Gorbachev hinted at a new Soviet proposal to reduce nuclear weapons during an interview with Time Magazine earlier this month, the Reagan administration has been pressing for details while publicly arguing that such statements are only propaganda unless presented for negotiation in Geneva.

The president repeated that theme Friday in sending U.S. negotiators back to Switzerland for the third round of talks. "Soviet leaders have recently given public indications that they may be considering significant nuclear reductions," Reagan said. "Now is the time for them to spell out their intentions," he added.

At Geneva, in the strategic weapons talks, the Soviet delegation has informally discussed approaches for reductions, including overall percentage cuts in numbers. In addition, they have mentioned limits on how much of each country's strategic forces could be in land-based missiles, submarine-based missiles and strategic bombers.

But the Soviet delegation has neither formally introduced a paper containing these ideas, nor presented any specific figures to indicate the depth and range of the cuts they have in mind and whether they apply to warheads as well as missiles.

The United States, on the other hand, has presented a draft treaty containing provisions for a one-third reduction in warheads and sharp reductions in Soviet intercontinental ballistic missiles, which Washington says present a first-strike threat. It also has proposed a complex formula to relate bombers to missiles.

In the forum dealing with space weapons, both sides have presented detailed interpretations on how they believe the 1972 Antiballistic Missile (ABM) treaty provides for research, development and deployment of new systems.

In the first two rounds of discussion, the Soviets maintained that the treaty barred even laboratory research on space defense systems. They based that argument on a single treaty word, which in English means "develop" but in Russian means to "create."

Gorbachev, in his Time interview, appeared to leave more room for negotiation on space systems, saying at one point that "research concerning space is going on and it will continue." But he added that in talking about restraints, "what we mean is the designing stage, when certain orders are given . . . for specific elements of the systems. And when they start building models . . . when they hold field tests."

Soviet officials in recent days have said Gorbachev's words represented a carefully conceived attempt to find a formulation that would satisfy the Reagan administration.

Diplomatic sources add, however, that beyond working out details of what may or may not be allowed in the research area, Moscow wants some reassurance on the long-range "intent" of the United States. One source pointed out that the Soviets see a basic conflict between the president's statements that he will abide by the ABM treaty, which bars a nationwide space-based ballistic missile defense, and his goal of a Strategic Defense Initiative to build such a system.

The thrust of Soviet official statements has been that the Reagan-Gorbachev meetings could reach significant agreements. One source said that by publicizing various Gorbachev proposals ahead of time, Moscow wanted to appear blameless in the event of failure in Geneva.

The source noted that there are other Soviet arms control proposals in which the Reagan administration showed no interest but which have supporters both inside the United States and in other parts of the world.

For example, he said that Shevardnadze would again ask the United States to join Gorbachev's moratorium on underground nuclear tests and resume negotiations for a complete ban on those tests. He will also push for some breakthrough on chemical weapons such as a weapons-free zone in Europe, a proposal that has great appeal in West Germany where U.S. chemical weapons are stockpiled.

When those proposals were first made public, the Reagan administration quickly rejected them. Soviet leaders have continued publicly to criticize Washington for its unwillingness to discuss those issues, particularly the underground testing moratorium.