Downey Rice, 65, a Washington lawyer whose work sometimes involved private investigations, died Sunday at Sibley Memorial Hospital following an apparent heart attack. He was stricken at his home in Washington.

One of Mr. Rice's best-known cases involved the apparent suicide of Sasha Bruce, daughter of the late Ambassador David K. E. Bruce. In September, after two years of work by Mr. Rice, a grand jury in Charlotte County, Va., brought an indictment against Marios Michaelides, Miss Bruce's husband, charging him with murder in her death. Michaelides also was charged with bigamy and embezzlement in the case.

Mr. Rice was a fourth-generation Washingtonian. He graduated from the old Columbus Law School, now part of Catholic University, and was appointed a special agent in the FBI in 1936. That was the beginning of his career both as an investigator and as a lawyer. He stayed in the FBI until 1945 and then opened a general law practice in Washington. It was through his law practice, which he continued until his death, that Mr. Rice got assignments such as the Bruce case.

"You see, I can do jackleg legal work, but having tasted some of the excitement, that's not enough." he said recently in an interview with The Washington Post. "There are 1,001 private eyes in the Yellow Pages, but very few of them have real legal training.

"You go to some little town and a sheriff doesn't recognize evidence that you do. You understand hearsay, he doesn't. You hear someone talking about a package in the mail and realize mail fraud."

Mr. Rice was stationed in New York during his FBI career. By his own account, much of his work with the bureau involved tracking down spies during World War II.

"We used to do all the things they think are evil today," he told The Post. "Following the guy around, listening on the phone, and if he left a note lying around, you'd be crazy not to read it. We invented the phrase 'black-bagging.' You'd get a camera and two gooseneck lamps and put 'em in a black bag."

After he returned to Washington and set up his own law office, Mr. Rice worked as a counsel for several Senate committees. Among them were the Senate investigating committee on organized crime, headed by the late Sen. Estes Kefauver in 1950 and 1951 and the hearings conducted by the late Sen. John McClellan into sports gambling in 1961.

In 1973, Mr. Rice was hired by the Pennsylvania legislature as a special counsel in an investigation on the administration of justice in that state.

He was a member of the Washington Criminal Justice Association and of the Society of Former Special Agents of the FBI. He was a member of the American and D.C. bar associations. He also was a member of the University Club and the President's Club of George Washington University.

Survivors include his wife, Ellen Smith Rice, of the home in Washington; a son, Michael, of Port Washington, N.Y.; a daughter, Ellen Sue Potter, of Birmingham, Mich.; two sisters, Patrice Howell, of Washington, and Evangeline Grant, of Seminole, Fla.; a brother, Fred Jr., of Chevy Chase, and nine grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Little Sisters of the Poor, P.O. Box 9318, Baltimore, 21228.