ASHINGTON, March 18 — Invoking history, law and the upper social strata of Washington, Justice Antonin Scalia said on Thursday that he would not remove himself from a case before the Supreme Court involving his good friend, Vice President Dick Cheney.

In a 21-page memorandum, a rare public explanation and rarer still for describing what it means to have friends in the highest of places, Justice Scalia said it was not improper that he hunted ducks in Louisiana with Mr. Cheney in January, just three weeks after the court agreed to consider the case.

Justice Scalia not only justified his participation in the case, he also disclosed new details of the trip. "I never hunted in the same blind with the vice president," he wrote.

He also recounted other cases in which presidents and justices socialized without concerns about appearance. Citing historical accounts, he wrote of a time when Justice Harlan F. Stone "tossed around a medicine ball with members of the Hoover administration mornings outside the White House," and when Chief Justice Fred M. Vinson "played poker with President Truman." And who could forget those days when Justice John Marshall Harlan and his wife sang hymns at the White House with President Rutherford B. Hayes or when Justice Byron R. White skied in Colorado with Attorney General Robert F. Kennedy?

In a more contemporary glimpse into the coziness of Washington's elite, Justice Scalia wrote, "A rule that required members of this court to remove themselves from cases in which the official actions of friends were at issue would be utterly disabling." Many justices, he said, were appointed to the court precisely because they were friends with the president or other senior officials.

Justice Scalia argued forcefully that friendship is a basis for recusal only "where the personal fortune or the personal freedom of the friend is at issue," not a friend's actions on behalf of the government. As a result, he wrote, he had no justification to step aside. A Supreme Court justice's decision on recusal is final and cannot be challenged.

The case before the court that involves Mr. Cheney is the effort by the Sierra Club to force him to provide information about the energy task force he led as the Bush administration, in its early months, was formulating environmental policy. After an appeals court ruled in favor of the Sierra Club and another plaintiff, Judicial Watch, a government watchdog group, the administration appealed to the Supreme Court on behalf of Mr. Cheney. The club, alone, petitioned Justice Scalia to step aside, arguing that his participation in the Louisiana trip created the appearance of favoritism undermining "the prestige and credibility of this court."

But in an obvious jab at the Sierra Club's reasoning that social contact by justices compromises their objectivity, Justice Scalia noted almost sarcastically that two days before the club opposed Mr. Cheney's appeal to the court, the club's lead lawyer in this case, Alan B. Morrison, a friend of Justice Scalia for nearly 30 years, invited him to address his Stanford Law School class.

"It was an open invitation," Mr. Morrison said, acknowledging Justice Scalia's reference as a not-so-subtle reminder that friendships transcend even political lines.

In his decision, Justice Scalia also took issue with critics who would assume he could not rule impartially simply because Mr. Cheney accepted his invitation to hunt ducks and he accepted Mr. Cheney's invitation to fly to Louisiana on a government jet. An account of the trip was published in The Daily Review in Morgan City, La., in early January, and The Los Angeles Times subsequently reported on the potential conflict of Justice Scalia serving on the case involving Mr. Cheney.

"If it is reasonable to think that a Supreme Court justice can be bought so cheap," Justice Scalia wrote, "the nation is in deeper trouble than I had imagined."

David Bookbinder, the Washington legal director for the Sierra Club, criticized Justice Scalia's decision, calling it "a splendid example of how secrecy corrodes public trust and the integrity of government."

"If Justice Scalia believes the facts as he laid them out," Mr. Bookbinder added, "he should have released them two months ago before the public started to ask questions."

The decision also drew strong criticism from Senator Patrick J. Leahy of Vermont, the ranking Democrat on the Judiciary Committee.

"There is no question that the very fact of this episode had raised appearance and impartiality issues," Mr. Leahy said. "To many, the very fact that this vacation weekend happened while this decision was pending is enough to make the situation quack like a duck."

Decisions on recusals by Supreme Court justices are not unusual, but most are voluntary, rather than in response to a petition from a litigant. And most come without comment, let alone one as long as Justice Scalia's.

In choosing to offer an expansive rationale, Justice Scalia provided colorful details of the January duck hunting trip as well as a snapshot of a friendship that began when he and Mr. Cheney both worked in the Ford administration. Justice Scalia was an assistant attorney general and Mr. Cheney was White House chief of staff.

The trip, he wrote, had been planned for the court's winter recess — and long before the court agreed to hear the case involving Mr. Cheney. Mr. Cheney accepted the invitation, noting that national security required him to fly in a government jet, and he offered Justice Scalia the chance to ride along if seats were available. They were, for Justice Scalia, for one of his sons and a son-in-law.

In Louisiana, Justice Scalia said the hunting party numbered about 13, including Mr. Cheney, his staff and security detail. They hunted over three days in two boats and ate all their meals together.

"Sleeping was in rooms of two or three, except for the vice president, who had his own quarters," Justice Scalia wrote. "Hunting was in two- or three-man blinds. As it turned out, I never hunted in the same blind with the vice president. Nor was I alone with him at any time during the trip, except, perhaps, for instances so brief and unintentional that I would not recall them — walking to or from a boat, perhaps, or going to or from dinner."

"Of course," he added, "we said not a word about the present case."

He and his relatives stayed in Louisiana two days longer than Mr. Cheney, Justice Scalia said, flying back to Washington on a commercial flight from New Orleans.

He wrote: "Since we were not returning with him, we purchased (because they were the least expensive) round-trip tickets that cost precisely what we would have paid if we had gone both down and back on commercial flights.

"In other words, none of us saved a cent by flying on the vice president's plane."