The No.2 man in the Justice Department, Deputy Atty. Gen. D. Lowell Jensen, was installed as a federal judge in San Francisco, with praise from his former boss, Atty. Gen Edwin Meese III. Meese and FBI director William Webster were among more than 100 well wishers in the federal courtroom where Jensen, 58, took the oath of office. Jensen was district attorney of Alameda County from 1969 until 1981, when he joined the Justice Department as assistant attorney general in charge of the Criminal Division. He was promoted to associate attorney general in 1983 and to deputy attorney general in 1985.