Soviet officials have passed the word that Foreign Minister Eduard Shevardnadze will propose to the Reagan administration this week that both superpowers reduce strategic nuclear missiles and warheads by 40 percent, according to a congressional source.

Shevardnadze will also propose that both countries agree not to put more than 60 percent of their overall nuclear strength into any one branch of their strategic forces -- that is, in either land-based or submarine-based missiles or bombers, Soviet spokesmen have told Americans in recent days.

In return, the Soviet foreign minister is expected to seek "significant" restraints on the U.S. Strategic Defense Initiative, President Reagan's "Star Wars" research program.

It was first reported nine days ago that Soviet sources had said Shevardnadze would be bringing concrete arms-control proposals on his current U.S. visit. Since then, the outlines of the Soviet package have been discussed with members of Congress by Soviet and U.S. government officials, one Capitol Hill source said.

A Reagan administration official said yesterday that officials were aware of the outline of the Shevardnadze package and are studying it. He added that there is skepticism "because it seems to have propaganda value" and the Soviets "are leaking it around before presenting it to the president."

Reagan said last week that he is unwilling to put restraints on SDI development and testing, other than those in the 1972 Anti-Ballistic Missile Treaty. He added that discussions with the Soviets should precede deployment of such a system, should it prove feasible.

The Reagan administration has also insisted repeatedly that the Soviet Union convert its vague talk about possible deep cuts in offensive weapons into concrete proposals. Soviet sources have said that Shevardnadze intends to fulfill that request and that the details would eventually be made public by Moscow.

"If there is no movement on arms control," one Soviet source said recently, "we want it known it was not our fault."

Each nation has accused the other in recents weeks of attempting to manipulate public opinion in this period before the summit meeting between Reagan and Soviet leader Mikhail Gorbachev, which will be held Nov. 19-20 in Geneva.

The Shevardnadze package is expected to provide the first details of the "radical proposals" on arms control that Gorbachev has said his government is willing to undertake. Gorbachev held out the possibility of such cuts in offensive arms during his meeting with U.S. senators earlier this month in Moscow and in his well-publicized interview with Time magazine.

Soviet sources said recently that if U.S. officials respond favorably by saying the proposals represent "a basis for negotiation," they will be presented at the Geneva arms talks, which resumed last week.

This source added, however, that if they are rejected "out of hand," as he said the White House had done with Gorbachev's earlier suggestion for a moratorium on underground nuclear testing, the proposals might not be presented in Geneva.

Told of the prospective Soviet offer, a White House spokesman said, "We will listen very carefully to whatever Shevardnadze brings with him. We have been calling for concrete and specific proposals . . . . We would be ready to respond positively to viable, concrete proposals."

Shevardnadze is scheduled to speak before the United Nations today and meet with Secretary of State George P. Shultz Wednesday in New York. He is scheduled to meet Reagan at the White House on Friday and will meet again with Shultz at the State Department.

Rep. Les Aspin (D-Wis.) told reporters at a breakfast yesterday that his "contacts" had told him Shevardnadze was "coming with significant numbers . . . , " but Aspin did not spell them out.

He also said if it were a viable proposal, the United States would have to "agree to some offense-for-defense trade," including a commitment on what Washington was "going to do in the future."

Aspin added that "it's pretty hard to see how a breakthrough will occur" given the president's position on SDI and the relatively brief time before the summit.

Until Reagan's news conference last week, several top administration arms-control experts were telling reporters and officials on Capitol Hill that they had begun to discuss what SDI restraints were possible if the Soviets offered to make deep reductions in strategic offensive weapons.