Secretary of State Cyrus R. Vance arrived yesterday pledging "perseverance and dedication" in pursuit of a new strategic arms limitation treaty (SALT) but was less certain than before that the goal can be achieved before the end of the year.
At an airport ceremony, Vance expressed hope that the talks, which begin in the Kremlin today, "will be able to build on the constructive movement" resulting from negotiations with Soviet Foreign Minister Andrei Gromyko in New York and Washington three weeks ago.
Gromyko, standing by Vance's side, said nothing.
The secretary of state, who consistently expressed belief in recent months that a SALT II treaty can be completed this year, is now saying only that he believes "its still possible (but) . . . I can't give any assurance."
Vance's views were made known by the senior American official who often briefs reporters abroad his plane on condition that he not be quoted by name.
According to the senior official, the "handful of issues" yet to be resolved in the superpower negotiations are in four areas:
"Details relating to cruise missiles."
"Details relating to the ban on new types" of land-based missile systems.
"Timing of reductions" in Soviet missile numbers required under the agreement.
"Satisfactory solutions of the remaining details on the Backfire," the Soviet medium-range bomber that has been a subject of controversy.
The senior American official would not spell out the differences involved.
Other sources, however, said the Soviet demand for strict range limitations on ground - and sea-launched cruise missiles - in return for dropping range limits on air-launched cruise missiles - is among the most difficult questions.
The ground-and sea-launched cruise missiles are of special interest to West Germany and other NATO countries which consider them a potential couterthreat to Soviet military power in Europe. For the same reason, limiting their range is of particular interest to the Soviet Union.
Another troublesome issue, according to the sources, is a Soviet proposal that no more than six multiple warheads (MIRVs) be permitted on "new types" of land-based missiles. The United States, which is ahead in MIRV technology, is reported to be holding out for a limit of 10 MIRVs on the "new types." Each side, as agreed in recent weeks, is permitted one "new type" of land-based intercontinental missile during the life of the treaty.