The Reagan administration intends to offer several new concessions on a proposed treaty with the Soviet Union eliminating medium-range and short-range nuclear missiles, but will not agree to renewed Soviet demands that the United States remove the warheads from 72 aging West German missiles, senior U.S. officials said yesterday.

The planned U.S. concessions will thus cover three of the four principal issues identified by Soviet army chief of staff, Marshal Sergei Akhromeyev, in Moscow yesterday as obstacles to a missile treaty and a summit meeting between President Reagan and Soviet leader Mikhail Gorbachev, the officials said.

With such a major issue unresolved, some officials were skeptical that a treaty might be concluded within the next two months, as the Soviets have suggested. Instead, one U.S. official said, it might be concluded by the end of the year after further discussions by U.S. and Soviet foreign ministers during the September meeting of the U.N. General Assembly.

There are no plans yet for such a Soviet-American ministerial meeting at the time of the session at the United Nations.

Several senior officials said the three issues on which the United States will compromise are: the timing for dismantling medium-range missiles; the question of shifting missiles based in Europe to ships floating offshore; and provisions for on-site inspections required to verify treaty compliance.

However, Reagan's national security adviser, Frank C. Carlucci, told reporters at breakfast yesterday that "we do not accept" the Soviet position that U.S. warheads for 72 Pershing IA short-range missiles owned by the West Germans must be withdrawn from Europe as part of the agreement eliminating all U.S. and Soviet short-range and medium-range missiles.

"We don't understand why they are putting this kind of obstacle in the way of an agreement," Carlucci said. "I see no reason why we would want to change our position and the president feels quite strongly on this issue," he added.

Carlucci's remarks were made before he learned of the renewed demand by chief Soviet negotiator Yuli Vorontsov in Moscow yesterday that the warheads be eliminated because they "present a real threat" to the Soviet Union and its East European allies. But a spokesman said later that Carlucci's remarks represent the U.S. position.

The administration yesterday began studying exactly how to modify the treaty verification and timing provisions included in its draft treaty in Geneva. The study began in response to the so-called "global, double-zero" missile endorsement by Gorbachev Wednesday, which was officially confirmed Thursday by Soviet negotiators in Geneva.

But several senior U.S. officials said the administration is already on the verge of formally deciding to modify its position and support the Soviet demand that 240 U.S. ground-launched cruise missiles in England, Italy, Belgium and Germany not be converted to cruise missiles based on ships at sea.

Instead, the officials said, the missiles would be destroyed under the agreement.

The officials also said there was broad, informal agreement within the administration to modify the U.S. position that the Soviets must reduce their 1,435 medium-range missile warheads in Europe and Asia to the current U.S. level of 348 warheads, before any reductions of the U.S. missiles occur.

The Soviets have insisted that some U.S. missile reductions must occur at the same time, and yesterday several senior U.S. officials said the United States would soon accede to this demand.

On verification, the officials said attainment of the "global, double-zero" in medium-range and short-range missiles would cause the administration to drop its demand that plants for production, assembly, and maintenance of these missiles be opened to continuous on-site U.S. inspection.

The officials cautioned, however, that no decision had been made within the administration on whether such on-site inspection would be needed on an interim basis during a prospective five-year period for missile reductions.

Any treaty will have to be sent to the Senate by "early next year" in order to obtain ratification before Reagan leaves office, Carlucci said.