Key Reagan administration officials are urging a swift U.S. response to a new Soviet arms-reduction offer in Geneva in an attempt to surmount unhappiness and confusion here and among U.S. allies over President Reagan's decision to abandon the limits on the SALT II agreement.

An interagency group is analyzing the Soviet offer, which was placed on the negotiating table in Geneva Wednesday, and drafting questions to be asked by U.S. negotiators, according to informed officials. A higher level meeting may be held next week to see whether a U.S. position can be forged before the current negotiating round ends June 26.

Differences of opinion about the seriousness of the Soviet proposal -- and how the United States should respond -- are developing in the administration. Several officials, including some in the Defense Department, have made no secret of their view that the Soviet offer is aimed at killing Reagan's Strategic Defense Initiative, or "Star Wars" missile defense research program. Other officials are wary of the potential effect on SDI but are hopeful that Moscow's offer could open the way for serious bargaining on major cuts in offensive arms.

Some details of the Soviet proposal, which offers reductions in strategic offensive arms in return for tighter restrictions on anti-missile systems such as SDI, became publicly available as the result of a briefing for journalists in Bonn by Viktor Karpov, chief Soviet negotiator in the arms talks, according to Reuter news agency.

The proposal, based on data in the Soviet briefing, a report in yesterday's New York Times and other information from U.S. officials in Washington, was in two parts:

In space defense, the Soviets are asking for a guarantee that the United States will adhere to the 1972 Anti-Ballistic Missile Treaty for another 15 to 20 years despite a clause in the agreement permitting either side to withdraw on six months' notice. There were other indications that the Soviets might settle for a 10-year extension, which would coincide with the earliest projections of U.S. capability to deploy initial elements of Star Wars.

The Soviets also proposed to nail down interpretations of permissible activity under the treaty to prohibit development of futuristic anti-ballistic missile systems such as that envisaged in Reagan's SDI. The Soviets also wish to define components and subcomponents under the treaty to close what they consider a loophole, which is being used to justify U.S. testing of SDI elements.

In offensive arms, the Soviets said they would drop an earlier demand that U.S. nuclear-armed fighter aircraft and carrier-based aircraft within reach of the Soviet Union be counted as strategic weapons subject to limitation under a new treaty. U.S. officials last fall described this as among the most unacceptable features of an initial Soviet offer for cuts up to 50 percent in strategic arms.

The Soviets now propose to permit submarine-launched long-range cruise missiles, which would have been banned under their earlier proposal, but to count them as strategic weapons.

Overall, the new Soviet proposal is reported to permit 8,000 strategic "nuclear charges" (missile warheads and bombs) on each side, compared with 6,000 apiece in Moscow's earlier proposal. This would work out to a cut of about one-third in strategic nuclear weapons, as an interim measure to greater cuts, rather than the 50 percent reductions once envisioned.

At the Soviet Embassy in Washington yesterday, Deputy Ambassador Oleg M. Sokolov refused to discuss details of the new offer on grounds of confidentiality. Sokolov said he hopes that the Reagan administration will have second thoughts about its decision to abandon the SALT II agreement and that such a reversal would aid the prospects for an arms accord as well as prospects for another summit meeting of Reagan and Soviet leader Mikhail Gorbachev. Sokolov said the Soviet Union "will take corresponding measures" if and when the United States exceeds the limits of SALT. "Our response will be proportionate," he said, but added that nothing would be done until the treaty limits are breached. This is not due to happen until late this year at the earliest.

Meanwhile, the controversy continued about Reagan's May 27 decision on the SALT II pact. Secretary of State George P. Shultz, speaking on a telecast to Europe sponsored by the U.S. Information Agency, rejected statements that the unratified SALT II treaty is "dead." Shultz said White House spokesman Larry Speakes had not used the word in briefing reporters Thursday. Shultz objected to those who "keep trying to insert that word, 'dead,' into other peoples' mouths."

Calling the treaty "obsolete," Shultz said Reagan sought "to substitute one form of restraint for another."

Speakes repeatedly said Thursday that "the SALT treaty no longer exists." When United Press International reporter Helen Thomas said to Reagan at a photo opportunity that "Larry Speakes told us very definitively that it is dead and yet you won't say it," the president replied, "I think you can trust what Larry Speakes said."

In another formulation yesterday, U.S. arms adviser Edward L. Rowny said, "SALT is behind us."