Dr. James Frenkil, the longtime chairman of Maryland's workmen's compensation board retired yesterday, hours before Gov. Harry Hughes was to ask the state ethics commission to review conflict-of-interest allegations against him.

Frenkil, 69, is founder and director of a clinic that serves many Maryland companies whose employes bring cases before the state Medical Board for Occupational Diseases. Despite mounting criticism of his industry ties, Frenkil said yesterday that the public controversy did not influence his decision to leave the post he has held for 28 years. "Not a bit," he said.

Frenkil refused to answer other questions about his retirement or to say whether he knew that Hughes had planned to request an ethics probe. He is the second member of the three-man board to retire in the last week, and like Dr. J. Howard Franz, who announced his retirement last Tuesday amid controversy over his industry ties, Frenkil defended his behavior on the board.

"I know of no cases of any conflict of interest on my part," Frenkil said in a letter delivered to Hughes yesterday. ". . . It has always been my disposition to be impartial to the interests of labor and industry and to weigh the merits of the individual case."

The medical board, which decides the cases of hundreds of workers who seek state compensation each year for job-related illnesses and injuries, currently has a backlog of about 800 cases, several officials said. That backlog and the ties of Franz and Frenkil to some of Maryland's major employers have brought the board under mounting attack from labor leaders who argue that injured Maryland workers often wait years before their cases are heard.

Some of the loudest criticism has come from the Baltimore Building and Construction Trades Council, whose president, Edward Courtney, has called publicly for Frenkil's ouster for alleged conflict of interest.

Frenkil describes his Central Medical Center as the eastern seaboard's largest industrial clinic. It serves employers and insurance companies from four Baltimore locations. The city of Baltimore is one of many major employers whose workers have received health services at the clinic.

Workers at Bethlehem Steel had filed a federal court suit seeking Franz' ouster, but it was made moot after Franz resigned last week. Franz has been a paid consultant to Bethlehem Steel for more than 20 years.

Courtney yesterday asserted that his union deserved most of the credit for the resignation of the two doctors, citing his testimony at a recent hearing held by a Hughes-appointed task force on workmen's compensation.

At the Dec. 16 hearing, Courtney charged that Central Medical Center held contracts with more than 1,000 companies in the building and construction fields. He also charged that in 250 of the 800 backlogged workmen's compensation cases, Frenkil's customers are the defendants. Frenkil refused yesterday to comment on those charges.

"I don't want to answer any questions of that kind," he said.

"The question of conflict has been raised in news accounts and in statements made by some labor leaders," said a Hughes aide. "The governor was in the process of referring the question of conflict to the state commission on ethics" at the time that Frenkil's letter arrived yesterday. The aide said Hughes had drafted a letter to the commission, which was to be delivered yesterday.

Frenkil, who has chaired the medical board since 1953, has said in interviews that he disqualifies himself from hearing cases involving his clinic's customers. He said he reviews such cases that his two colleagues hear, and that he signs the board's final orders.

Frenkil said in his letter that he is resigning largely because of the board's increasing workload and predicted that the backlog will worsen because its staff has not been increased. "Despite my appeals for assistance, no relief has been forthcoming, resulting in the present situation, which is beyond the ability of the board to manage," he wrote.

The longtime chairman also charged that the recent attacks on him and the board are part of a campaign to have the board abolished altogether. Although he denied in a brief interview that the attacks had forced him to resign, Frenkil wrote in his letter: "The assault is so vicious and so full of false innuendoes and false information that I find it unthinkable to subject myself to deal with these groups."

Panos said Hughes expects to receive a report next month from his task force on workmen's compensation, which was instructed to study ways to solve the problem of the claims backlog. The governor, who is on vacation until Jan. 8, has written letters to the deans of the medical schools at Johns Hopkins University and the University of Maryland and the state medical society to ask for nominations to fill the places of Frenkil and Franz, according to the governor's press secretary, Lou Panos.

Frenkil's resignation is effective Jan. 15. Hundreds of pending workmen's compensation claims could be thrown into limbo if no new board member is named before then, since the three-member board by law cannot act without the vote of a two-man majority.

Many doctors contend that it is impossible for the board to be fully independent, since most doctors with experience in the field of occupational disease have done some consulting for unions, government or business.