Secretary of State Cyrus Vance held nearly six hours of "constructive" talks with Soviet Foreign Minister Andrei Gromyko yesterday with no sign of a breakthrough toward completion of a new strategic arms limitation treaty.

U.S. sources indicated that movement toward a new SALT agreement, if any, would probably have to come in a meeting expected this afternoon between Vance and Soviet leader Leonid Brezhnev.

State Department spokesman Hodding Carter III said Vance had not been in touch by telephone with President Carter and did not anticipate that he would be, an indication that no flurry of intensive bargaining is anticipated.

The spokesman called yesterday morning's talks in the Kremlin, involving full delegations of about 10 officials on each side, "a standard opening" meeting. The afternoon meeting was of a smaller group: Vance, Gromyko and only two advisers for each. After the later session, spokesman Carter passed along Vance's characterization of the talks as "constructive."

The meetings here so far have been devoted entirely to a new arms limitation treaty, according to Carter, suggesting that political problems between the two countries in other areas have not been the stumbling block that some anticipated. He said specifically that there had been no discussion of the U.S. president's decision to order production of some components of the neutron bomb, an action which has evoked major criticism in the Soviet press.

Vance began his eighth round of SALT talks with Gromyko with no predictions that the remaining issues can be settled on this trip, and with less certainty than in the past that a SALT II can be completed this year.

As usual, the Soviet press has taken little note of the meetings while they are in process.

The secretary of state, after continuing the talks with Gromyko, plans to leave Moscow Tuesday for Washington.