An administration task force is studying possible changes in the U.S. proposal now on the negotiating table in Geneva in the Strategic Arms Reduction Talks (START) with the Soviet Union.

Officials say the group--composed of officials from the State Department, the Pentagon, the White House National Security Council staff and the Arms Control and Disarmament Agency--might agree on alterations to the existing proposal before the talks resume June 8.

They stress, however, that no decision has been made and caution that there are complicating factors that could extend the Washington deliberations.

The idea behind the study is to bring any new U.S. proposal into line with the recommendations of the presidential advisory commission on the MX and other U.S. nuclear forces that reported to Reagan April 11 and whose recommendations Reagan adopted April 19. The interagency group began its work shortly after Reagan's action, officials said.

Among the commission's recommendations was one that called for the administration to "reassess" a portion of its START proposal, which calls for specific limits on the missiles in each country's arsenal.

The commission said that it was an emphasis on reducing the number of missiles that leads both countries to try to cram as many warheads as possible on each missile. This increases the risk that either side may fire quickly in a crisis rather than risk losing its multiple-warhead weapons.

The panel said it is really warheads that matter and that the U.S. proposal should focus on limiting them. It also recommended that, for the long haul, the United States try to develop a small, single-warhead missile that would be a less inviting target than current U.S. missiles and that could be protected from attack, in part by making it mobile and in part through a negotiated limit on warheads with Moscow.

The administration's current START proposal does contain a mutual limit of 5,000 warheads for each side. But it also calls for reducing the number of missiles on each side to 850.

It is this 850 figure that would probably have to be eliminated in any new proposal. The administration might also add some proposals that would attempt to restrict the overall lifting power, or throw-weight, of Soviet missiles, which currently are much more powerful than their U.S. counterparts.

One complication, however, is that some officials who support the overall recommendations of the special commission have concerns about the future of the small missile.

At issue is whether it can be made safe from attack; how many might be needed; and whether future arms control arrangements would allow verification of the number of these small, and probably mobile, missiles that are actually fielded by either side