Arthur A. Marshall, Prince George's County's controversial chief prosecutor since 1962, lost last night his bid for a Circuit Court judgeship. He had challenged the two most recent appointees to the bench, G.R. Hovey Johnson and Arthur M. Ahalt, who retained their seats.

Maryland voters, meanwhile, approved overwhelmingly a state constitutional amendment preventing anyone unable to vote from running for office. The amendment will prevent former state senator Tommie Broadwater, of Glenarden, from seeking his old seat because Broadwater, who is on probation after serving four months in jail for food stamp fraud, is unable to vote.

Prince George's County voters supported the amendment 100,360 to 25,505.

In Prince George's school board races, three incumbents retained their seats.

In the hotly contested judgeship race, Ahalt led with 108,284 votes, followed by Johnson with 100,212 and Marshall with 90,181.

Marshall told supporters in Upper Marlboro last night he would not yet concede since 7,500 absentee ballots were to be counted. "This is a people's campaign," he said, hinting he might challenge other sitting judges in 1986.

Marshall was a formidable opponent for the two judges, who were appointed by Gov. Harry Hughes in 1982. Under Maryland law. Such appointments must be confirmed by the voters after one year.

Circuit Court judges running for retention are rarely challenged, but Marshall's decision to throw his hat into the ring made the three-way battle for the two judgeships one of the hottest local races this year.

The county bar association backed the two incumbent judges, as did county and state elected officials.

But Marshall, 54, had alienated many lawyers with his well-known maverick streak.

When Marshall applied four years ago for a seat on the state's Court of Special Appeals, he said he was told by the nominating panel that he needed more experience in civil cases. Incensed, Marshall decided to place his qualifications directly before the voters.

A staunch Democrat, Marshall lost his party's primary but came in second in the Republican primary. Marshall said that large numbers of blacks came out to vote for Jesse Jackson and the sitting judges because Johnson is black.

Judge Johnson, 53, is a former Green Beret and a retired Army colonel who went to Georgetown University Law School after the service. He began his legal career in 1979 as a Prince George's public defender. He won second place in the Democratic primary, behind Ahalt, who finished first in both primaries.

Ahalt, 43, was born and raised in Prince George's and attended law school at American University. He worked for two well-known county law firms before his appointment to the bench.

While drawing less attention than the judgeship race, county school board contests offered the possibility of a major change in board membership. Six of the nine seats were at stake, and only 3rd-District incumbent Catherine Burch ran unopposed.

Serious contests were waged for the remaining five seats, three of them held by incumbents.

Incumbent Doris A. Eugene won in District 1 with 9,979 votes to 7,392 for Mary Ellen Jenkins. In District 7, incumbent Sarah J. Johnson defeated her opponent, John H. Francis, 10,236 to 5,638.

District 9 incumbent Norman H. Saunders beat challenger Marcy Canavan, 9,576 to 8,220 .

In District 4, New Carollton attorney Thomas Hendershot defeated William J. McEwen, 9,223 to 8,565. And in District 6, Barbara Fletcher Martin had tallied 9,272 votes compared with John Rosser's 5,403.

Candidates had, without exception, campaigned for reduced class size. It is an issue that has gained attention as the school board has grappled with TRIM, the county's cap on property tax collections. The average county class size ranges from 28 to 30 students, but many classes are larger, according to school officials.

Most candidates, arguing for better teacher salaries, textbooks and staffing, supported the measure to amend TRIM and, theoretically, free up more money for schools.