In the final days before the November election, the 9-month-old judgeship race in Prince George's County has heated up, with State's Attorney Arthur A. Marshall charging that his opponents, judges Arthur M. Ahalt and G. R. Hovey Johnson, are violating ethics and federal elections rules.

To date, no government agency has substantiated Marshall's contentions, which the judges have characterized as "desperation tactics."

Marshall has sent letters to the county's Democratic Central Committee, the Federal Election Commission and the Judicial Ethics Committee, charging that Ahalt and Johnson are illegally commingling their campaign funds.

He said the money was being used to print sample ballots that will include the names of the county's Democratic congressman, Steny Hoyer, and presidential candidate Walter F. Mondale.

"This is supposed to be a nonpartisan election," said Marshall. He said that he also thought it improper for the judges to be wearing Mondale/Ferraro buttons at a recent Democratic rally.

Marshall and the judges, all registered Democrats, were candidates in both party primaries, but Marshall won second place in the Republican race behind Ahalt and a surprising third in the Democratic primary.

County elections administrator Robert J. Antonetti said this week that Maryland law requires the judges' race to be nonpartisan, meaning that names of judgeship and school board candidates must appear on the ballot without party identification. But, he said, "I can't see anything wrong with endorsements" of any of the candidates by either party during the campaign leading up to the election.

The Judicial Ethics Committee declined to respond to Marshall's allegations, and the Federal Elections Commission is currently looking into the matter. Democratic Central Committee Chairman Gary Alexander called Marshall's letter "a frivolous complaint" and said the committee has received no money from the judges.

According to the judges' campaign manager, William Connelly, each of the judges has contributed $5,000 to help with the printing of campaign literature sponsored by the Democratic Central Committee. But he said the money was paid directly to the printers.

Ahalt said campaign workers have been advised by an FEC spokesman that payment in this manner will avoid the commingling problem. Hoyer will also help pay for printing the pamphlets.

Johnson said recently that Marshall's charges "are totally without any credibility" and that he believes the accusations are a ploy "to gain publicity."

Ahalt said Marshall was "making charges up because he can't answer the issues." Both judges insist that the only issue in this campaign is whether they have done their jobs well and should be retained in office.

Ahalt, 43, and Johnson, 52, both respected as lawyers but lacking in political experience, were appointed to the bench by Gov. Harry Hughes in 1982. Under state law, voters this fall must confirm the appointments for a 15-year term.

Judges are rarely challenged in elections, but this time Marshall, 54, who has been the county's outspoken chief prosecutor for 23 years, has thrown himself into the fray. He is generally critical of the judiciary, charging that they are often not responsive to the public.

Marshall said recently that he believes the two sitting judges are precluded by the Canons of Judicial Ethics from appearing on the Democratic sample ballot. Marshall, whose name appears on Republican literature being distributed in the county, argues that the same rules do not apply to him.

"I'm not a judge; I'm not bound by the canons of judicial ethics," he said.

According to an American Bar Association opinion issued in 1961, judges should usually refrain from partisan politics but "active participation by an incumbent judge in contributing to the funds of the party which nominated him . . . is proper."

There have been other criticisms of Marshall's campaign strategies, such as his suggestion that people vote only for him. Although the November ballot will instruct voters to "vote for no more than two" of the three candidates, Marshall campaign posters urge them to "Vote for One!"

Of that process, called 'single shooting,' Marshall explained: "If you vote for me once, it's like voting for me twice. I need the votes."

"It's the most underhanded thing I've ever seen," said one local attorney after he saw a Marshall "Vote for One!" sign.

Although Marshall has no specific criticisms of Ahalt and Johnson, Marshall says that his experience as a prosecutor makes him better qualified to be a judge.

"I've been practicing law longer than these two put together," Marshall said at a recent community meeting in College Park.

Johnson, a former Army colonel, has been an attorney for six years. Ahalt, a Prince George's native, has been in the legal profession for 17 years. Both have received overwhelming support from the local and state bar associations, nearly all of the county's elected officials and a number of civic associations.

Marshall, angered at being turned down three years ago by a nominating committee in his bid for state Court of Special Appeals, maintains that the electorate, not selection committees or governors, should choose judges.

Some of the staunchest support for Marshall's law-and-order campaign comes from the Stephanie Roper Committee, a victims' rights organization formed after the brutal 1982 murder of the Frostburg State college student.

Marshall, who maintains that judges are too lenient, has spoken out against the short sentences that a judge in another county gave Roper's killers. Marshall has won permission to try the men, Jack Jones and Jerry Lee Beatty, in Prince George's on additional rape charges related to Roper's death.

Marshall recently hired Kurt Wolfgang, a former law student and currently an adviser to the Roper Committee, to handle public relations for the state's attorney's office and his campaign. His alliance with the committee makes some people uncomfortable, but he said, "I'd rather be obliged to the Roper Committee than to the lawyers," who support the judges.

Assessing public opinion on the race is difficult because, except for lawyers and politicians, few people are talking about it.

Bennie Thayer, a local businessman who was the Maryland chairman for Jesse Jackson's campaign, said he is concerned about keeping Johnson, who is black, on the bench. But he added that he is worried that the election may not be "as cut and dried for the sitting judges as I thought it would be."

Thayer said the Mondale campaign has not kept "the fervor of the Democratic voters high," and therefore he is not sure how potential Reagan voters will vote in the local election.

County executive Parris N. Glendening agreed with Thayer. "It's a close race, but a very unpredictable race," he said.