MOSCOW (AP) _ Jan Vagris was elected Tuesday to head the Communist Party in the Baltic republic of Latvia, succeeding Boris Pugo who was transferred to Moscow last week.

Vagris had served as chairman of the Presidium of the Latvian Supreme Soviet, or legislature, since 1985. The official Tass news agency said he was elected first secretary of the Latvian Communist Party at a plenary meeting of the Latvian Central Committee,

Pugo, who had headed the Latvian party since April 1984, was promoted last Friday to become chairman of the Soviet Communist Party's Control Committee, which oversees the maintenance of party discipline.

Pugo replaced Mikhail S. Solomentsev, 75, who retired.

Tass said Pugo made a speech at the Central Committee meeting Tuesday in Riga but it gave no details.

Under political reforms pursued by Soviet leader Mikhail S. Gorbachev, local Communist Party chiefs are to stand for election.

Vagris' election as the party chief in Latvia was believed to be the first instance under Gorbachev's program where the current head of a legislature was subsequently named leader of the local party rather than the other way around.

Gorbachev, the Soviet party's general secretary, introduced major changes last week, retiring President Andrei A. Gromyko and succeeding him as head of state.

Tass said Vagris, 56 and an engineer by training, ''is well conversant with economic problems.''

''He pays much attention to social issues, to studying the daily concerns and needs of common people and extending democracy,'' the agency said.