Patrick Coleman O'Donoghue, 49, a labor lawyer in Washington for more than 20 years, died Monday at Albert Einstein Hospital in Philadelphia. He had suffered a stroke in July while vacationing at Bethany Beach, Del.

Mr. O'Donoghue was the senior partner in the law firm of O'Donoghue and O'Donoghue, founded by his father, Martin F. O'Donoghue, also a well-known labor lawyer, who died in 1973.

The younger Mr. O'Donoghue had joined his father's firm in 1956 and since then mainly had represented international and local unions in the building and construction trades.

At the time of his death, he was general counsel to the United Association of Plumbers and Pipefitters, the International Union of Elevator Constructors and the Metal Trades Department of the AFL-CIO.

Mr. O'Donoghue was born in Washington. He was a graduate of Gonzaga High School and Holy Cross College and received a law degree and master of law degree from Georgetown University. He had been an adjunct professor at Georgetown Law School since 1959.

He had been counsel to the Board of Trustees of Trinity College for many years. He had served on the Chairman's Task Force on the National Labor Relations Board, created in 1976 for a one-year study of the board, which led to labor reform.

Mr. O'Donoghue was active on a number of major committees of the D.C. Bar Association and the American Bar Association.

After finishing law school, he served in the Army Judge Advocate General's Corps.

He was a member of the National Association of College and University Attorneys, the Friendly Sons of St. Patrick and the Congressional Country Club.

He is survived by his wife, the former Fanchon Heinrich, and five children, Brian, Coleman, Blaine, Leigh and Karen, all of the home in Sumner, Md.; his mother, Mrs. Martin F. O'Donoghue, of Washington, and three brothers, Martin F. Jr., of McLean, Dr. J. Levin, of Chicago, and Dr. J. Morgan, of Sumner.