Soviet aid to Kabul is knot for superpower statesmen to untangle

President Reagan hopes that the Soviets will be pulling out of Afghanistan by the time he holds a summit meeting with General Secretary Mikhail Gorbachev in Moscow. But that scenario has hit a snag - the United States insistence that Moscow end all military aid to its clients in Kabul as the US halts its support for the Afghan resistance groups.

Resolution of this crucial issue is high on the agenda of this week's talks between Secretary of State George Shultz and Soviet Foreign Minister Eduard Shevardnadze. Setting a date for the summit and making headway on the strategic nuclear arms negotiations are also objectives of their three-day meeting, which were due to begin yesterday, a day earlier than planned.

``The most important thing is if we can solve the remaining things on Afghanistan and get a date for the summit,'' a senior administration official says.

Diplomatic observers voice concern that, if the Afghanistan issue is not resolved, it could cast a cloud over the Moscow summit meeting, expected to be scheduled late in May.

It was not until the summit in Washington in December that the President raised the aid-cutoff issue with Mr. Gorbachev. The US had already agreed in the UN-sponsored talks on Afghanistan that it would halt its military assistance to the Afghan guerrillas 60 days after an agreement was signed and a Soviet withdrawal was under way. But the subject of Soviet military aid to the Kabul regime apparently was not discussed.

``We thought it was implicit - a `symmetry of obligations,''' the senior US official says.

Members of Congress are pressing the President to stand firm on the aid issue. The Senate in February passed a resolution opposing a cutoff of US help to the Afghan rebels before the Soviets ended their occupation. In response to these concerns, Reagan sent a letter to the Senate reaffirming that any US and Soviet commitments in an Afghan settlement had to be ``symmetrical.''

``The congressional attitude makes it hard to bend much,'' the senior US official says. But the President's initial stance was equally hard-line.

The US position has caused dismay in Moscow, which had stated that it would begin withdrawing its troops from Afghanistan as early as May 15. There is speculation that the Soviet timetable may now be set back. But reports from Moscow indicate that Mr. Shevardnadze has in hand some proposals to break the impasse over the aid issue.

Another major area of discussion is the draft strategic nuclear arms treaty. High US and Soviet officials say publicly that it will be possible to reach an agreement by the time of the Moscow summit but that it will be difficult.

``A lot of good work has been done on the documents that will be reviewed by the ministers - the protocols on verification, destruction of weapons, and so on,'' a ranking US official says. ``But there are still a lot of brackets in the draft treaty.''

Among the unresolved issues are the sublimits on individual categories of weapons. US officials say that, if the two sides can agree on how to count air-launched cruise missiles carried aboard bombers (ALCMS), the sublimits on other systems will fall into place.

Also at issue are the so-called SLCMS, or submarine-launched cruise missiles, which can carry either conventional or nuclear warheads. The Soviets want to include these weapons in an agreement; the US is prepared to do so if verification measures can be found.

Land-based mobile missiles are another problem area. The US has called for a total ban on mobile missiles but is expected to abandon that position if agreement can be reached on a verification plan. The proposed ban was never deemed serious by arms experts in light of the American interest in putting the MX missile on a mobile system and developing the single-warhead Midgetman missile.

Mr. Shevardnadze and Secretary Shultz are also expected to discuss the US peace initiative in the Middle East and developments in Nicaragua. The two men are said to have established a friendly, workmanlike relationship. This is the second of three ministerial meetings scheduled before the Moscow summit.