A broad hint of future Soviet accommodation on Afghanistan and a lack of movement on nuclear and space arms were important substantive features of the first U.S.-Soviet summit in six years, U.S. officials said today.

The central accomplishments of the the meetings of President Reagan and Soviet leader Mikhail Gorbachev, from all indications available here, was to restart the process of top-level dialogue between the two nuclear superpowers, to begin a personal relationship between the two leaders and to return to positive aspects of U.S.-Soviet bilateral ties for the first time since the 1970s.

U.S. experts here tended to agree with Reagan's statement at the joint ceremony with Gorbachev today that "the real report card on Geneva will not come in for months or even years." In general, very few shifts in substantive positions were discernable in the two days of meetings, which included intense person-to-person discussion between the two leaders and authorized future summit meetings on a regular basis.

Perhaps most interesting were the omissions -- the expected issues that the Soviets chose not to emphasize. Officials said there was only a brief mention of extension of the SALT II treaty, which Moscow had proposed in advance, and of the U.S. reinterpretation of the 1972 Antiballistic Missile Treaty. There was no discussion of the line between permissible research and banned testing of the Strategic Defense Initiative (SDI), and no mention was made at all, according to U.S. officials, of the leaked letter of Secretary of Defense Caspar W. Weinberger that had dominated American press attention as the summit meeting began.

The most intriguing surprise to some U.S. participants was the change in the tone and, to some degree, the substance of Gorbachev's discussion of the Soviet occupation of Afghanistan. The Soviet move into that country in the last days of 1979 was a major factor in the hardening U.S. position toward Moscow and the demise of detente.

Secretary of State George P. Shultz said Afghanistan "was treated at some length" as part of "really a very good discussion on the regional issues" dividing Moscow and Washington. Another senior official who sat in the talks, but who spoke to reporters on a not-for-attribution basis, gave his personal opinion that some progress might be made toward settling the issue of Afghanistan and said the question might be handled "more intensively and less visibly" in the future.

The most notable development, according to U.S. sources, was Gorbachev's unemotional tone about the Afghan war, in which the Soviet Union has engaged about 115,000 troops, and his expressed desire to work quietly to find a way out.

One official said Gorbachev did not mention U.S. support for the Afghan insurgents or the involvement of Pakistan, which are among the most persistent themes in Soviet public statements on the issue.

Gorbachev did not make known any new Soviet efforts to find a way out of Afghanistan, but the tenor of this discussion, and the seemingly significant omissions, prompted speculation about shifts to come.

The major obstacle on arms control, as expected, was the strong Soviet opposition to SDI. Gorbachev condemned it as "weapons in space," and Reagan responded by calling it "a shield in space," according to an official.

In a private talk in his villa's poolhouse Tuesday afternoon, Reagan reportedly handed Gorbachev a four-point draft for joint "guidelines" to be issued to give impetus to the nuclear and space negotiators. Point three, which dealt with SDI, may have been the reason that the Soviets did not accept it.

As proposed to Gorbachev, point three made it explicit that programs of strategic antimissile defense could be pursued within the confines permitted by the 1972 ntiballistic Missile Treaty, and that the two nations would work cooperatively on the relationship of the strategic offense and strategic defense.

The Soviets not only rejected this, according to U.S. sources, but sought to the very end to obtain agreement in the final joint statement calling for a stoppage of work, including research, on SDI, sometimes called "Star Wars."

The U.S. delegation would not agree to this, and left open the possibility that there would be no joint statement, but only separate statements by the two sides, if the Soviets persisted. The argument was not finally settled until 4:15 a.m., according to officials involved.

The sparse language that was issued by the two sides in the joint statement announced by Reagan and Gorbachev did little to advance the nuclear and space arms negotiations. The agreement to "accelerate" the talks was lacking in specifics. The stated intention to seek 50 percent reductions as "appropriately applied" left unresolved the large-scale differences about what nuclear systems are to be cut and even whether the weaponry is to be measured in warheads or, as the Soviets prefer, "nuclear charges." The statement did endorse the idea of a spearate, or as the Soviets preferred to call it, an "interim" accord on intermediate-range weapons in Europe, which previously had been endorsed by both nations.

The fact that the Soviets seemed eager to have a joint statement by the two leaders, and in general to make the summit appear to be a success, was attributed by U.S. sources to Gorbachev's desire for a good start with the United States to shore up his position on the eve of the Communist Party Congress. It seemed important to him as well, these officials said, to begin on the right footing with the first American president he has ever met.