Secretary of State Cyrus R. Vance and Soviet Ambassador Anatoliy F. Dobrynin held their fourth SALT meeting in two weeks last night amid reports that all major outstanding issues have been resolved and only secondary questions and details of summit-signing remain.

State Department spokesman Tom Reston said after the one-hour meeting that the two men "continue slogging away" at the remaining difference on a new strategic arms limitation treaty (SALT).

Reston said they would meet again this afternoon, the first time meetings were scheduled on successive days since the Vance-Dobrynin round of talks opened early this year.

Reston said the two officials talked mostly about SALT but did not discuss when and where a Soviet-American summit would occur.

Earlier yesterday, department spokesman Hodding Carter said any announcement of a summit would await "a moment advantageous at the highest levels of the two capitals." Reporters took that to mean that no announcement is likely before President Carter returns Sunday afternoon from his Georgia vacation.

Mindful of the many dashed hopes and overptimistic reports that the SALT accord was completed officials refused to predict when the talks might end.

Spokesman Carter said before last night's meeting that "real problems" regarding SALT remain to be worked out before a summit meeting of President Carter and Soviet President Leonid Brezhnev can be scheduled to sign the document. Other officials said Vance and Dobrynin are now left with SALT issues that previously were considered secondary or even minor.

The two principal issues reported to have been resolved in recent days are:

The precise definition of the one "new type" of land-based intercontinental ballistic missile permitted to each side under the treaty. The Russians originally asked for an allowable reduction in missile characteristics of 20 percent without considering a weapon to be a "new type." The United States had proposed 5 percent allowable variation. The Soviets essentially acceded to the U.S. position, according to the reports.

Restrictions on the encoding of missile testing information, or telemetry. The Soviets have agreed not to encode testing information when this would impede the verification of SALT provisions, A lengthy exchange of statements and messages has aimed at a precise understanding of how this restriction would apply in practice.

One of the secondary problems now being discussed is a Soviet missile capability, displayed in a late December test, to launch about 12 reentry vehicles (warheads). Ten is the limit for land-based missiles under the proposed treaty.

U.S. officials initially reacted with concern to the Soviet display of prowess, but now American military services are reported to be urging that they be permitted to develop the same capability. A possible settlement would be an agreement that any reentry vehicles above 10 be launched in such a way that they could clearly be distinguished as dummy or decoy warheads rather than armed ones.

Several SALT issues will remain to be officially resolved at the CarterBrezhnev summit. These include an exchange of letters on the Soviet swing-wing bomber known in the West as the Backfire. It is not considered a strategic bomber under the terms of treaty but it will be the subject of some Soviet assurances. An exchange of statements on the telemetry issue is also likely.

Senior administration officials said Carter hopes to discuss with Brezhnev the objectives and procedures for SALT III negotiations aimed at greater reductions. Carter is also reported to seek a substantive review of SALT II at the summit and to have some hope that it could be improved, even as it is about to be signed.