Deputy Attorney General D. Lowell Jensen, a respected former prosecutor who manages the Justice Department on a daily basis, is expected to leave soon to become a federal district judge in northern California, according to department sources.

The departure of Jensen, a low-key manager who works mainly behind the scenes, would leave his longtime friend Attorney General Edwin Meese III with a major decision on how to fill the department's No. 2 post.

Jensen is expected to have little trouble winning Senate confirmation. In the 1960s, he worked with Meese as a deputy district attorney in Alameda County, Calif., and went on to become district attorney.

In 1981, President Reagan named Jensen as assistant attorney general in charge of the department's Criminal Division. He moved up to associate attorney general, the No. 3 job, in late 1983, and was tapped as Meese's deputy last spring after Meese became attorney general.

An aide to Sen. Pete Wilson (R-Calif.), who would make a recommendation to the White House for the district court vacancy in San Francisco, said Wilson's screening committee is still reviewing candidates and that a final decision is weeks away. He would not confirm that Jensen, who has known the senator for some time, is among the candidates and stressed that no one has been selected.

Jensen declined comment yesterday.

A Justice Department official said Jensen "would be hard to beat" as a judicial candidate, and several people who work with him have been planning on his expected departure.

Although Jensen would have to clear an FBI background check and evaluation by the American Bar Association, another Justice official said that "this is one that could race through. He's got a lot of friends in the ABA and the Senate."

The news set off a round of speculation about possible replacements, but a senior Justice official denied rumors that Stephen S. Trott, head of the Criminal Division, would take Jensen's job. The No. 3 official is former New York lawyer Arnold I. Burns, who has been on the job less than three months.

Jensen keeps a firm hand on the department during Meese's frequent travels around the country and abroad. His three confirmation hearings carried no trace of the controversy that involved William Bradford Reynolds, who failed in his bid to succeed him as associate attorney general.