MOSCOW, JAN. 6 -- Soviet Deputy Foreign Minister Yuli Vorontsov is expected to relinquish his post as chief negotiator at the Geneva disarmament talks when they start up again this month, according to Soviet sources.

The sources said the diplomat, who is now viewed as Moscow's top troubleshooter, was being freed from his negotiating duties to allow him to spend more time on regional issues, specifically Afghanistan, which in recent days has emerged as a focus of Soviet diplomatic activity.

Soviet Foreign Minister Eduard Shevardnadze returned today from Kabul after an unexpected two-day working visit to the Afghan capital.

Vorontsov will be replaced by Alexei Obukhov, now Vorontsov's deputy, the Soviet sources said.

Obukhov is a veteran Soviet negotiator who previously headed delegations at the talks on intermediate-range and strategic nuclear weapons.

Vorontsov, a former Soviet ambassador to Paris, was put in charge of the Soviet delegation in Geneva after the U.S.-Soviet summit meeting in Reykjavik, Iceland.

His arrival at the talks in Geneva was seen as a sign that the Soviets were preparing for serious negotiations.

Vorontsov's more informal, businesslike style was credited for facilitating the process that led to the agreement last fall on removal of shorter- and medium-range nuclear missiles.

Described by Soviet officials as having direct access to Kremlin policymakers, Vorontsov has been highly visible recently in efforts to improve Soviet relations with Iran.

The change at the top of the Soviet delegation in Geneva comes as the two sides begin to try to produce a treaty to cut strategic weapons by 50 percent in time for a scheduled summit meeting in Moscow later this year between President Reagan and Soviet leader Mikhail Gorbachev.