Rep. W.C. (Dan) Daniel, 73, a Democrat from Southside Virginia who was in his 10th term in the House of Representatives, died yesterday at the University of Virginia Medical Center in Charlottesville.

A Danville resident known for his conservative votes and views, the white-haired, craggy-featured congressman was a champion of a strong defense as a senior member of the Armed Services Committee and chairman of the subcommittee on readiness.

Hospital officials said the 19-year congressman died at 5:20 p.m. of an "unusually severe" hemorrhage caused by a dissection, or peeling and weakening, of the aorta, the body's main artery.

On Tuesday, the self-made sharecropper's son, who had not faced major party opposition at the polls since 1970, announced that he would not seek reelection this fall because of heart trouble.

Rep. Daniel, who spoke for the largely rural 5th District, had been hospitalized several times last year and visited the U-Va. medical center on Tuesday for further tests.

The Chatham, Va., native was the senior member of Virginia's congressional delegation and the last survivor in Congress of the Byrd machine, which had once dominated the state's politics.

In announcing his plans to retire, he said he was no longer able to give a "100 percent effort."

It was not clear whether the dissection of his aorta, the trunk artery that carries blood directly from the heart, was related to his previously diagnosed problems, which apparently involved heart valves and the blood vessels supplying the heart itself, hospital officials said.

They said he was admitted to the hospital at 1:20 p.m. yesterday "suffering from some distress."

In 1985, Rep. Daniel was investigated by the House Ethics Committee for accepting 23 free airplane rides, provided by Beech Aircraft Corp., while urging Congress to direct the Pentagon to buy 24 Beech C12 airplanes.

The investigation was expanded to look into whether he submitted vouchers for travel to his district by car when he had been flown there.

The panel found that Rep. Daniel had improperly accepted free airplane rides but recommended no penalty after he repaid the company and amended his financial disclosure statements.

Rep. Daniel said "anybody who knows me knows I'm not going to give my vote for an airplane ride somewhere."

On the readiness subcommittee, Rep. Daniel, who served in the Navy during World War II, was known for efforts to ensure proper maintenance for armed forces facilities and equipment. He was a former national commander of the American Legion.

A Democrat who often supported President Reagan, Rep. Daniel was a vigorous anticommunist who warned in debate against killing funding for the MX missile.

If the funds were denied, he said, "we may as well begin now to give up our institution of freedom, tear up and throw away what is left of the Constitution, dismantle our republic and convert the United States into a satellite of the Soviet Union."

The only member of Virginia's congressional delegation without a college degree, and a former textile mill hand, he became a Dan River Mills executive before his 1968 election, and had headed the State Chamber of Commerce and served in the House of Delegates.

Survivors include his wife, the former Ruby McGregor, and one son, Jimmy.