A Washington lawyer pleaded guilty, yesterday in U.S. District Court to a charge he cashed a check from an insurance company that was intended for one of his clients in an accident case.

The attorney, John M. Newsome of 2300 Ross Rd., Silver Spring, entered a guilty plea before Judge John G. Penn to one count of false pretenses. Prosecutors said they would drop a second charge of mail fraud against Newsome as part of a plea bargain arrangement.

The conviction stems from a massive federal investigation into alleged insurance fraud by several Washington doctors and lawyers, according to Assistant U.S. Attorney Jeffrey T. Demerath.

Newsome, 53, has practiced law in the District and Maryland for 20 years. He was disbarred from practice in the District by the D.C. Court of Appeals last year on unrelated charges.

The conviction yesterday resulted from a 1978 traffic accident case Newsome handled for a woman who had been injured in an Autorama taxicab in which she had been a passenger.

Newsome negotiated a settlement on the woman's behalf with the insurance company which represented the cab company. The agreement Newsome worked out provided for the woman, Amy Quiss of Silver Spring, to be paid $1,650 in return for her agreement not to file suit against the company.

Prosecutors claimed, however, that Newsome never informed Quiss of the settlement, endorsed the insurance company's check with both his and her name, and deposited it into an account he controlled at a Washington bank. He also signed the agreement that she would not sue the insurance company, which he had not been authorized to do by his client, prosecutors said.

Quiss learned of the settlement only after the insurance firm. Amalgamated Insurance Co., routinely informed her that it had paid Newsome as part of the agreement.

After Quiss said she had never been informed by Newsome of the settlement or received money due her, the insurance company informed prosecutors.

Newsome, who will be sentenced Oct. 15, could receive a maximum of one year in jail and a $1,000 fine. As part of the plea arrangement with prosecutors, Newsome will pay Quiss restitution of about $750.

Newsome was disbarred in 1978 by the D.C. Court of Appeals on charges that he misappropriated a client's funds in an estate case.