Prince George's County Executive Lawrence J. Hogan yesterday nominated a veteran Republican official and a retired Army administrator unknown in local government to fill important county jobs.

Hogan nominated former Washington Suburban Sanitary Commission chairman Lawrence L. Brooks to fill the WSSC commissioners' position vacated last month by Marvin L. Gay, who resigned. Hogan also named a career U.S. Army employe, John Earl Mann, as his choice for county personnel director.

The appointments were the first Hogan has made in more than a month, after a flurry of appointments - some of them controversial - in his first weeks in office. After three months as executive, Hogan has yet to decide on several county department chiefs, including detention center director and public works and transportation director.

County Council members and other officials said Hogan made a logical and almost predictable choice in nominating Brooks, one of the county's most prominent black Republicans, to the WSSC in place of Gay, who is also black.

Mann, they said, was unknown to both Hogan and the council before the search for a personnel director began. But Hogan said he submitted both appointments to the council for comment before announcing them, and it was expected that council members would not seriously contest them.

Brooks, 60, was the first black to be appointed to the WSSC. He was nominated by then-Executive William W. Gullett in 1972. Brooks was appointed only after a lengthy and bitter strugle between Gullett, a Republican, and the council.

Yesterday, however, State Sen. John J. Garrity, who voted against Brooks as a council member in 1972, said "I would vote to approve him now. He has the experience that is needed, he knows the problems of the community, and he did a good job before."

State Sen. Tommie Broadwater, a leader of the county's black Democratc politicians, added that Brooks was "a good choice for Hogan. He's a Republican, and he wanted to appoint another Republican, and there are not many qualified black Republicans around," Broadwater said.

Some county black leaders said, however, that they thought Brooks lacked aggressiveness in pursuing minority issues on the WSSC, which controls water and sewer networks in suburban Maryland and has much influence over the kind of growth that occurs in Montgomery and Prince George's counties.