The Soviet Union, signaling that it still hopes for agreement with President Reagan on space weapons constraints, gave the United States for the first time a detailed written proposal to bar testing of sophisticated missile defense technologies in space, U.S. and Soviet officials said yesterday.

Soviet negotiator Alexei Obukhov told reporters in Geneva that the new initiative was a "major proposal" aimed at "preventing an arms race in outer space" and "strengthening" the 1972 Antiballistic Missile (ABM) treaty. The offer comes amid new optimism for prospects of a U.S.-Soviet pact banning intermediate-range missiles.

A knowledgeable U.S. official said the space weapons proposal included a comprehensive list -- which the Soviets had not previously endorsed at the Geneva negotiations -- of seven or eight types of weapons to be barred from space testing by mutual agreement, including lasers or rockets capable of shooting down ballistic missiles.

Several U.S. officials immediately criticized the new list, which they said was clearly aimed at constraining the U.S. missile defense research effort, the Strategic Defense Initiative (SDI), or "Star Wars," program, for which a series of elaborate space tests has been planned.

"Our initial reaction is one of disappointment," said State Department spokesman Charles E. Redman. "The Soviet draft appears to reflect positions they have held throughout the course of the negotiations."

Kenneth L. Adelman, director of the U.S. Arms Control and Disarmament Agency, said, "It did not strike me as anything new or terribly interesting." A similar, but shorter, paper was presented to Secretary of State George P. Shultz in Moscow last April, Adelman said.

But one knowledgeable official also said it was very similar to a previous proposal by senior State Department arms control adviser Paul H. Nitze, which was rejected by Reagan, that the two sides reach a detailed agreement on space weapons testing barred by the ABM treaty.

"The Soviets have clearly thrown the ball back in our court, hoping to breathe fresh life" into the long-stalled missile defense negotiations, the official said.

The list of categories of space weapons tests to be banned by the agreement was said to be drawn from recent conversations between independent U.S. arms control experts -- acting with the knowledge of the State Department -- and senior Soviet scientists.

Nitze has long argued without success within the administration that an agreement with the Soviets on such a detailed list could potentially permit important SDI research to continue, while at the same time satisfy Soviet concerns that SDI deployments be put off to the future.

Nitze believes that a resolution of this dispute would solidify congressional support for SDI and enable the United States and the Soviet Union to reach a broader and more important agreement on strategic arms reductions. Several members of the U.S. negotiating team have taken a similar view.

But others within the administration, such as Adelman and Secretary of Defense Caspar W. Weinberger have insisted that such detailed discussions would inevitably lead to constraints on SDI that would postpone the deployment of sophisticated missile defenses in space beyond the earliest point at which it could occur. They have also said that the United States would be unable to verify Soviet compliance with the limitations.

As a result, U.S. negotiators are not presently authorized to discuss such detailed limitations on space tests, a policy that was reaffirmed by the White House as recently as last month.

The Reagan administration has instead been willing to agree only that the United States would not withdraw from the ABM treaty to begin space weapons deployments for at least seven years, during which it would abide by a controversial, permissive interpretation of the ABM treaty's research constraints.

The Soviets, in contrast, would couple tough research constraints with a 10-year period in which neither side could withdraw from the treaty, to be followed by additional negotiations before either side could begin space weapon deployments.