Retired Supreme Court justice Potter Stewart was listed in critical condition yesterday in a New Hampshire hospital after suffering a stroke on Monday.

Stewart, 70, who retired from the court in 1981, was admitted to Dartmouth-Hitchcock Medical Center in Hanover after falling ill at his daughter's home in nearby Putney, Vt., according to Supreme Court press officer Toni House.

Stewart, a moderate Republican appointed to the court in 1958 by President Dwight D. Eisenhower, was for years a critical swing vote in rulings on major social issues. His seat was taken in 1981 by Justice Sandra Day O'Connor.

Stewart, a member of a prominent Cincinnati family and son of a Republican mayor there, was a member of the city council and a vice mayor in the early 1950s. He was the youngest federal judge in the country when he was appointed to the 6th U.S. Circuit Court of Appeals in 1954.

Eisenhower gave Stewart a recess appointment to the high court in October 1958 and sent his name to the Senate for formal ratification in January 1959.

Stewart and then-Justice John Marshall Harlan, his colleague and mentor, represented a pragmatic conservatism that tended to assess each case on the facts, rather than through a rigid ideological prism. As such, Stewart was often seen as a conservative on some issues and a liberal on others, especially matters involving free speech and the press.

Stewart joined liberal rulings such as the one-person, one-vote ruling, Baker v. Carr, and the 1973 decision legalizing abortion, but he dissented from rulings allowing government contract "set-asides" to ensure that some went to minorities and from the court's ruling outlawing organized school prayer.

One reason Stewart gave for retiring at the relatively young age of 66 was that he wanted to leave the court "in good health." But his health began to deteriorate in 1982 after he broke several ribs and chipped his collarbone in a fall at his New Hampshire home.

Sources said yesterday he also had Parkinson's disease, a degenerative nervous-system disorder. He nevertheless had worked almost daily in an office at the Supreme Court building since his retirement, assisting circuit courts with their cases, being an international arbitrator and serving on presidential commissions.