New Gorbachev Spokesman Faces Test : Soviet Union: The former party functionary is charged with convincing the world of his boss’ continued influence.

Soviet President Mikhail S. Gorbachev on Monday named a dapper polyglot and former high-ranking Communist Party functionary to be his new official spokesman.

Andrei Grachev, 50, fated to become a frequent presence on American television screens, takes on a far different job from that carried out by his predecessor, Vitaly N. Ignatenko, who was transferred by Gorbachev to head the official Soviet news agency Tass.

A large part--perhaps the major one--of Grachev’s responsibilities will lie in convincing his country and the world that Gorbachev is still a vital player in Soviet domestic and foreign policy and that all is now not being decided by Russian Federation President Boris N. Yeltsin.

Grachev told Tass that he has identified two main tasks--”on the one hand, to inform the public most fully, accurately and promptly about the Soviet president’s activity and course and, on the other, to inform the head of state himself about how his policy is perceived in our country and abroad.”

Until the political shake-up caused by the August putsch, Grachev had been deputy chief of the International Department of the Communist Party’s now-disbanded Central Committee. His superior, Valentin M. Falin, had his home searched after the rightist coup d’etat , but Falin was not implicated in the abortive attempt to overthrow Gorbachev.

Trim and a very elegant dresser, Grachev was a frequent sight at high-level Soviet diplomatic meetings, where, with poise and polish, he could articulately present the Kremlin’s world view to participants or reporters in English, French and Spanish.

He is a graduate of the Moscow State Institute of Foreign Relations and, like Foreign Minister Boris D. Pankin, worked when young for the Communist Youth League’s newspaper, Komsomolskaya Pravda.

Grachev also studied Vietnamese at one time and served as the Soviet representative to the World Federation of Democratic Youth, a Moscow-financed front organization that used to marshal support among young people worldwide for the Kremlin’s policies.

Grachev indirectly owes his job to the bloodless purges carried out to punish people and organizations implicated in the anti-Gorbachev putsch. The previous director of Tass, which was one of the right-wing plotters’ chief conduits to the public, was fired and replaced by Ignatenko last month.

Grachev told Tass that what attracted him to the new job was its “keen combination of information and politics, both internal and foreign.” He promised to hold his first meeting with the Moscow press corps in the next few days.

He has written books on political extremism and terrorism. According to Tass, his wife is an art critic, specializing in modern art, while their son is a fourth-year student of journalism at Moscow State University.