A U.S.-Soviet dispute over the scope of on-site inspections is the principal obstacle to final agreement on a 100-page treaty to eliminate medium- and shorter-range nuclear missiles, U.S. arms-control experts said yesterday.

Dozens of minor details relating to the sensitive topic of treaty verification also need to be worked out before the treaty will be ready for signing by President Reagan and Soviet leader Mikhail Gorbachev in Washington Dec. 7, experts here said.

But they said the public commitment by leaders on both sides to finish it by then will probably increase flexibility.

U.S. officials said the negotiators of the superpowers have not yet agreed on the type or location of facilities that will be subject to on-site inspections aimed at resolving suspicions of noncompliance with the agreement.

Assistant Secretary of State Rozanne L. Ridgway recently told a House Foreign Affairs subcommittee that the Reagan administration believes suspicious, missile-related activities anywhere in the United States or the Soviet Union can trigger such an inspection, while the Soviets seek access to "any U.S. base, any manufacturing plant, public or private, anywhere in the world," including Western Europe.

The United States has held to its consistent theme that it cannot bargain such rights for other countries where it has such bases, especially where leasing agreements and shared facilities are involved, Ridgway said.

The Soviets have also sought inspection rights at the production site for U.S. ground-launched cruise missiles to be eliminated under the agreement.

But the Reagan administration has agreed to grant such access only to facilities related to the Pershing II ballistic missile that would also be eliminated.

The Pentagon is opposed to letting Soviet inspectors visit the cruise missile production plant because other missiles capable of being launched from bombers and submarines are also produced at the plant but not covered by the agreement.

The Soviets, for their part, have been reluctant to allow up to 15 on-site inspections annually, as U.S. negotiators have sought, preferring instead a maximum of 10 inspections annually in the first five years after the treaty takes effect, and then only two or three inspections each year thereafter.

Negotiators also have yet to work out the number of experts that could participate in on-site inspections, the type of equipment they can carry or how quickly they can gain access to the site of a suspected violation.