Administration hard-liners are studying a possible new U.S. arms control position that would limit the number of U.S. and Soviet mobile strategic missiles and set geographic restrictions on where such weapons could roam "to make deployment more verifiable," according to one informed administration official.

Such a proposal would be in reply to the latest Soviet arms offer and would represent a modification of the current U.S. position, which calls for a ban on all strategic mobile missiles.

The United States called for a ban on mobile strategic missiles last November as part of the superpower jockeying before the summit meeting between President Reagan and Soviet leader Mikhail Gorbachev. At the time, most U.S. experts considered the proposal simply a bargaining chip unacceptable to Moscow, which has deployed one type of strategic mobile missile, the SS25, and has another, the SS24, that may be operational by the end of the year.

But some Pentagon officials believe that, even if the Soviets reject the idea of a ban on mobile missiles, Moscow may agree to limits. The Soviets are prepared to designate deployment areas for their strategic mobile missiles, to allow monitoring of the launcher assembly areas for such missiles while they are in the field, and to put the missiles in sheltered garages with sliding roofs that would allow surveillance by reconnaissance satellites, according to sources on Capitol Hill. In addition, sources said, the Soviets have said they will mark the railroad cars that carry SS24 missiles to plainly differentiate them from other railroad cars.

Although some of the administration's most conservative arms control officials believe the Soviet proposal deserves no response, their current emphasis on mobile missiles represents an attempt to prevent compromises on space and defensive weaponry by giving a little ground on offensive weapons, according to informed sources. Defense Department civilians in particular, including Defense Secretary Caspar W. Weinberger, believe the United States should not budge from its current position on defense and space weapons.

The Soviet offer presented earlier this summer, one Pentagon official said recently, "is inadequate on the offensive side and eventual death to Reagan's Strategic Defense Initiative SDI," because Moscow wants to limit such missile defense programs.

Outside the Pentagon, however, some more moderate officials believe the United States should take into account the most recent Soviet suggestion that both parties agree to adhere to the 1972 Antiballistic Missile (ABM) Treaty for 15 to 20 years. Some strategists believe that the United States could safely agree to observe the treaty for five or six years, since SDI research is not far enough advanced to permit deployment during that time period anyway.

While Reagan and his top advisers are described in news accounts as wrestling over how to respond positively to Gorbachev's most recent letter and the latest Soviet arms offer, interagency specialists at lower levels are still arguing over the meaning of the technical details in Moscow's proposals.

The current situation suggests the old bromide about U.S.-Soviet arms talks, that the toughest negotiations take place not between the diplomats in Geneva but in Washington among the various U.S. government agencies and officials.

For example, State and Defense Department officials do not even agree on the extent to which the recent Moscow offer represents concessions.

The Soviets dropped their earlier insistence that U.S. nuclear-capable fighter-bombers in Europe be included in the total tally of strategic forces. Some officials considered that a concession. However, Pentagon strategists argue that the new Soviet proposal is seriously flawed because it would freeze the number of bombers and prohibit their movement to other bases, and may prevent modernization.

Another aspect of the Soviet offer that some see as a concession is Moscow's apparent willingness to permit SDI research, in conjunction with a pledge by Washington to continue adhering to the ABM Treaty.

So-called hard-line strategists, however, argue that U.S. agreement to such a provision would undercut SDI funding on Capitol Hill. Also, there are objections to proposed Soviet restrictions on testing and development of SDI weapons.

In addition, the latest Soviet offer calls for a ban on antisatellite weapons and any space-based system that could hit targets on Earth. The Reagan administration has consistently opposed an antisatellite ban and one of the leading SDI systems now under study envisions destroying enemy missiles with mirrors which would reflect laser beams toward Earth.