The Soviet Union refused to discuss U.S. offers to limit offensive nuclear arms during the first round of Geneva negotiations, which ended last week, and "backtracked" from earlier Soviet offers, reporters were told yesterday as the U.S. delegation met with President Reagan.

Moscow's negotiators insisted on "banning" President Reagan's Strategic Defense Initiative, or "Star Wars" plan, as a first step toward any reduction in the offensive area, according to a senior administration official.

No progress was made toward resolving the disputes over compliance with earlier arms agreements, notably the big Siberian radar now under construction, reporters were told.

Disclosing details of the first six weeks of the Geneva negotiations, the official said in a State Department briefing that Soviet intransigence had been anticipated and that it probably will continue for the forseeable future.

Despite the bleak result of the first round, said the official, there is no sign that either side will break off the talks, which are expected to resume at the end of May.

The official cannot be named under the terms of the State Department briefing. An on-the-record speech on much the same material is to be made at the National Press Club today by Paul H. Nitze, senior adviser on arms negotiations and a key figure in working out the U.S. strategy.

Reagan, following a brief meeting with Ambassadors Max M. Kampelman, John G. Tower and Maynard W. Glitman, his chief Geneva negotiators, said the talks are complicated and difficult. Nevertheless, he said in a statement that "we find ourselves in the best position to achieve meaningful arms limitations that has existed in a generation. With patience, strength and Western solidarity, we will succeed."

Secretary of State George P. Shultz, in an interview with The Washington Post, said he will discuss the arms questions in a meeting May 14 in Vienna with Soviet Foreign Minister Andrei Gromyko, but held out no promise of a breakthrough on that occasion. "I don't think people should try to draw too much in the way of conclusions from an initial round of negotiations," Shultz said.

The glum U.S. assessment of the opening round paralleled that of Soviet leader Mikhail Gorbachev before the Communist Party Central Committee last Tuesday. "The completed first stage of the Geneva talks already indicates that Washington does not seek agreement with the Soviet Union . . . it refuses, in general, to discuss the question of preventing the arms race from spreading to space simultaneously with the discussion of the question of nuclear arms limitation and reduction," Gorbachev said.

Both sides began the talks insisting on confidentiality as a sign of seriousness of purpose and an essential ingredient of real progress.

Yesterday's "background briefing," the most extensive U.S. account so far made public, was justified on grounds that Gorbachev has discussed the negotiations in two recent speeches and that Gromyko had set forth Soviet positions in a January news conference.

The Soviet approach to the first Geneva round "concentrated on providing a base for their propaganda efforts," according to the U.S. briefer. He expressed the view that Moscow will seek to force Washington to make concessions under the pressures of public opinion here and in Western Europe, and that the Soviet position will change only if and when the public campaign fails.

In returning to Geneva after boycotting arms negotiations for more than a year, the Soviets insisted that these are "new negotiations." It was suggested that this is part of the Soviets' rationale for revising their earlier arms positions.

Despite Gorbachev's statement last Friday that the Soviet "by way of an opening move" had suggested 25 percent cuts in offensive strategic arsenals, the Soviet side did not make such a proposal in Geneva, the official said.

A proposal for a major cut in launchers, but not in warheads, had been made by the Soviets in earlier negotiations. Previously they also had been willing to discuss numerical limits on air-launched cruise missiles, but now are insisting that these weapons be banned, the official said.

The Soviets in earlier intermediate-range negotiations had discussed a freeze on the number of SS20 missiles in Asia, in response to U.S. insistence on "global limits." This apparently has been withdrawn, according to the official.

Both sides argued their opposing positions on space in Geneva. The U.S. side proposed to discuss the introduction of exotic defensive systems of the future with a view toward possible amendment of the 1972 Anti-Ballistic Missile Treaty, the official said. The Soviets, he said, called for a ban on "space strike arms" including banning any research leading to their development.