John J. Abt, a lawyer who spent most of his career as chief counsel to the Communist Party in the United States, died on Saturday at the Columbia-Greene Medical Center in Hudson, N.Y. He was 87 years old and lived in Manhattan.

He died as a result of a stroke, his family said.

In the early 1950's, Mr. Abt and the late Vito Marcantonio, then state chairman of the American Labor Party, were retained to test the constitutionality of the Internal Security Act, also known as the McCarran Act. The act, passed in 1950 over President Harry S. Truman's veto, requires registration of Communists and other "subversive" groups and bars Communists from holding Federal jobs and passports.

Arguing before the Supreme Court on the constitutionality of the act in 1960, Mr. Abt said the statute represented "an attempt without precedent in this country to enforce conformity by suppressing association and advocacy." In 1961, however, the Court sustained the section of the act requiring Communist-action organizations to register with the Government, 5 to 4.

Although he lost that battle, Mr. Abt did win a unanimous Supreme Court ruling in 1965 that individuals may invoke their constitutional privilege against self-incrimination and refuse to register with the Government as members of the Communist Party. Mr. Abt considered this his greatest legal victory.

At his 80th birthday celebration, Mr. Abt a slender, quick-witted man with a small, brush mustache, said he had been a member of the Communist Party for 50 years.

"I am sure that this announcement will surprise no one here tonight," he said. "But it seems to me a rather sad commentary on the state of the freedom of political association in this country that I had to wait for half a century after the event before I felt free, publicly and proudly, to confirm a fact which anyone who knows anything at all about me has assumed to be true for lo, these many years ."

John Jacob Abt was born in Chicago on May 1, 1904, into what he described in a 1989 interview as a "bourgeois family." His father was a Yale graduate and he himself was a graduate of the University of Chicago, Phi Beta Kappa and summa cum laude, and from its law school.

From 1927 to 1933, he practiced real-estate and corporate law in Chicago.

In the early 1930's, inspired by the New Deal, he moved to Washington and joined the Agricultural Adjustment Administration. He then became assistant general counsel for the Works Progress Administration, and in 1936 and 1937 was chief counsel for the Senate Civil Liberties Investigating Committee.

In 1937, he married Jessica Smith, editor of The New World Review magazine, then Soviet Russia Today, and a year later, moved to New York. She died in 1983. The couple had no children. Refused to Testify

In 1948, Mr. Abt became a key worker for the Progressive Party in the Presidential campaign of Henry A. Wallace. That year, a Time magazine editor named Whittaker Chambers testified before the House Un-American Activities Committee about what he said was a prewar Communist underground in the Federal Government. One of the men he named as a member of a "cell" in the Agricultural Adjustment Administration in the early 1930's was John J. Abt. Mr. Abt refused to testify before the committee.

In 1953, as chief counsel, he represented the Communist Party in a case in which the New York Board of Regents sought to bar party members from holding jobs in the schools. The Board of Regents lost.

Four years later, he was back in the news when Col. Rudolf Abel, the Soviet agent, asked Mr. Abt to defend him against charges that he transmitted United States secrets to the Soviet Government. Mr. Abt turned him down.

The day after President John F. Kennedy was assassinated in November 1963, Lee Harvey Oswald, accused as the killer, asked to be allowed to hire Mr. Abt to defend him. Before Mr. Abt could accept or reject the bid, Mr. Oswald was shot and killed by Jack Ruby.

Mr. Abt is survived by his wife, the former Vita Barsky, and a stepdaughter, Judy Dodson of Sparkhill, N.Y.

John Abt