The Maryland attorney general recommended yesterday that Prince George's delegate-elect Francis W. White "stand aside" when the new legislature is sworn into office until it can be determined whether he legally lives in a rented room in the district he was elected to represent.

Benjamin L. Cardin, the incoming speaker of the House, said the challenge to White's residency is "unprecedented." He said he would go along with the recommendation of the attorney general's office if questions about White's residency are determined to have "some merit."

Under Maryland law, a delegate must take up residence in his district no later than six months before the election. White, according to public documents, failed to register to vote in his district until less than three months before the primary, did not change his car registration until September and was receiving his payroll checks at another location in early October.

White has said, however, that within a week of separating from his wife in July 1977 he moved in with old friends from whom he rented a room in Kettering, in the 76th Legislative District. "I have lived there continuously since," he said. "I live there. I go to sleep there. That is where I reside."

"Mr. White should stand aside until the House has the opportunity to CONSIDER THIS MATTER," SAID THE LEGAL OPINION SIGNED Thursday by Deputy Attorney General George A. Nilson and Assistant Attorney General Richard E. i/srael.

"This is an unfortunate situation," said Cardin (D-Baltimore) who also is an attorney. "I'm sorry to see this type of issue is one of the first to confront the new legislature. But we have a constitutional responsibility, and we will carry it out."

The residency requirement is part of the Maryland Constitution, and the state's highest court has ruled that each house of the legislature has "exclusive authority" to decide whether a member meets the requirement.

White, the former chairman of the Prince George's County Council, ran for delegate after he fell into disfavor with party leaders and was dropped from the official county party ticket. There was no answer yesterday at the telephone number listed for White at 33 Thurston Dr. in Kettering, where he says he maintains his residence.

For most of the last 20 years, White lived with his wife and three children at 42 Lakeside Dr. In Greenbelt, a town in the 24th District. That's where he lived when he served as the mayor of Greenbelt and when he was twice elected -- in 1970 and 1974 -- to the Prince George's County Council.

In July 1977, White has said, he separated from his wife and moved in with old friends, Richard and Carol Spencer, at the Kettering address.

Two defeated opponents, however, charged that he didn't actually live in Kettering. An aide to a Prince George's coiuncilman said she had more success reaching White at an address in Mitchellville. But Carol Spencer said, "Mr. White has been here every night for the past year, except for a couple of times when he went out of town on business."

"The controlling factor (in determining residency) is the person's intent," the attorney general's opinion said, "which may be more satisfactorily shown by what a person does rather than what is said... In order to preserve the authority of the House to pass on the challenged qualifications... I advise that he should stand aside when the oath is administered to members whose elections and qualifications are not challenged."

"It's the first time I've heard any good news," save Frank J. Broschart II, a high school psychology teacher who White edged out by 180 votes in the primary. "Since Sept. 15 we've done everything we could to get this case before some kind of body."

Broschart appealed on three occasions to the county elections board, took his case to Prince Georges' Circuit Court and went to see Maryland special prosecutor Gerald Glass. Finally, on Dec. 13, he petitioned John Hanson Briscoe, who is until Jan. 10 the speaker of the House of Delegates. Briscoe, in turn, requested the attorney general's opinion.

"Following the election of the speaker and the adoption of rules," the state lawyers said, Broscharter's petition should "be laid before the House for its consideration."

Cardin, whose election is a formality, said yesterday the matter will be discussed next week with other incoming legislative leaders. Cardin said he wants the attorney general's office to determine before Jan. 10 whether the petition is frivolous or has "some merit." If frivolous, he said, White should take office Jan. 10.

If White is not immediately sworn and is ultimately disqualified, Broschart said yesterday he would ask to be named to the seat, or would seek a new election.