Joseph Forer, 75, a noted Washington trial attorney for more than 30 years who became known for his work in cases involving civil rights and liberties and who was a founder of the National Lawyers Guild, died June 20 at Holy Cross Hospital after a stroke and heart attack.

Mr. Forer was a partner in the old Washington firm of Forer & Rein for 33 years before retiring in 1979. He received the American Civil Liberties Union's Henry E. Edgerton Award in 1979.

The National Lawyers Guild, which now handles civil rights, civil liberties and labor law cases, was best known for representing leftists during the 1940s and 1950s.

It was during those years that Mr. Forer came to prominence as a forceful, combative and effective defender of unpopular causes. He represented many people whose beliefs and actions were under fire from executive agencies or congressional committees, including such figures as Gus Hall, who was then the leader of the Communist Party USA.

With New York lawyer John Abt, Mr. Forer fought in federal court against the McCarran Internal Security Act, which required Communist Party members and members of communist "front" organizations to register with the government. They were eventually successful in getting most of the act struck down.

He also represented the pressmen's union in its unsuccessful strike against The Washington Post in the mid-1970s, and was counsel for several other labor groups, including the United Electrical Workers Union.

In the field of civil rights, Mr. Forer led the fight that resulted in a 1953 Supreme Court ruling that upheld city antidiscrimination laws on the books since the 1870s. As a result, the city's segregated restaurants and hotels were forced to serve black customers.

His best-known criminal defense, popularly known as the Giles Brothers case, resulted in the freeing in 1967 of three black men who had been sentenced to death in 1961 for raping a white woman. Though he was not involved in the original defense, Mr. Forer's appeal work resulted in the Supreme Court ordering a new trial for two of the men, and in Montgomery County -- after the discovery of new evidence favorable to the defendants -- declining to try the case. The third man was pardoned by Maryland governor Spiro T. Agnew.

Mr. Forer, who lived in Silver Spring, was a native of Trenton, N.J. He was a graduate of Rutgers University and earned his law degree at the University of Pennsylvania.

He moved to Washington in the mid-1930s and became an attorney with the National Labor Relations Board. During World War II, he was a lawyer and high-ranking official in the enforcement division of the old Office of Price Administration. In 1946, he retired from government service and entered into the private practice of law.

Survivors include his wife, Florence, of Silver Spring; a daughter, Dr. Jane F. Gentleman of Ottawa; three brothers, Bernard, of Sarasota, Fla., Morris and Robert, both of Princeton, N.J., and two grandchildren.