F. Edward Hebert, 78, a congressman from Louisiana for 36 years who was known as one of the most powerful men in the House as the crusty, colorful Armed Services Committee chairman from 1971-75, died last night in New Orleans.

A onetime newspaper city editor who won fame for investigating scandal in New Orleans, the bear-like, 6-foot-2 Herbert was known during his chairmanship as a firm friend of the Pentagon, and as a stubborn, hawkish defender of often unpopular military spending programs.

In a stunning break with tradition, his fellow Democrats disposed him as chairman Jan. 16, 1975, in a revolt against seniority made possible by the votes of reform-minded freshman elected in the aftermath of Watergate.

The defeat came as a severe blow to Mr. Hebert's spirit and will. Along with the slow healing of a broken arm suffered in fall later in 1975, and eye problems that left him virtually blind, the loss of chairmanship was believed to be a major factor in the New Orleans native's decision not to seek reelection to the seat he had first won in 1940.

Mr. Hebert -- whose name he was fond of reminding people was pronounced a-bare, in the French style -- died at 6 p.m. EST in a New Orleans hospital after a heart attack.

An outspoken, often flamboyant and witty man, Mr. Hebert made it clear on the day he announced he would not seek reelection that he was unapologetic about his support of a national defense second to none.

"There has never been any secret about my position on national defense and the security of this nation," he said. "I accepted the responsibility of defending that positon without hesitation . . ."

Among the accomplishments he cited were expansion of ROTC programs, equalization of the armed services academies and "far-reaching elimination of waste in military spending."

Wise in the ways of power, Mr. Hebert, who insisted "I've never asked for anything," watched appreciatively as military installations and Departmnet of Defense dollars gravitated toward Louisiana and his district.

By the end of his 18 terms in Congress, his district included an F. Edward Hebert Federal Building, an F. Edward Hebert Defense Complex and an F. Edward Hebert Naval Hospital.

The 250-bed hospital, which was built for $22 million and cost about $7.7 million per year to operate since its Dec. 7, 1976, opening, was almost never used.

Felix Edward Hebert, the son of a streetcar motorman and a former school teacher, was born Oct. 12, 1901, and attended public and parochial schools in New Orleans before entering Tulane University there.

At Tulane, Mr. Hebert, who studied law for three years, was a university debating champion and sports editor of the school paper. At the same time he worked as assistant sports editor of the New Orleans Times-Picayune.

By 1929 he was political editor of the New Orleans States, with a front-page column that he continued for nine years. In 1937 he was promoted to city editor.

Proceeding from tips received by the paper, Mr. Hebert directed an investigation of scandals involving the political machine of Louisiana's former governor and senator Huey P. Long.

Stories written by Mr. Hebert on the scandals helped his paper win an award for "courage in journalism" given by the Sigma Delta Chi journalism fraternity, and propelled him into politics.

Mr. Hebert built a reputation in Congress as an investigator. In the late 1950s he won publicity as chairman of an investigative subcommittee that turned up evidence of waste in military contracts.

During the Vietnam War, he headed an investigation of the Mylai massacre, and produced a report that accused both military and State Department officials in Vietnam of trying to cover up the evidence.

On most issues, however, he was known as a staunch defender of the military who often was in conflict with civilian officials at the Pentagon, whom he did not find sufficiently aggressive in pursing the Vietnam War.

While Congress bore a share of the responsibility for the "tragedy of Vietnam," Mr. Hebert said in 1975, the responsibility also lay with "previous administrations and a Defense secretary who sent our boys with their arms tied behind their backs in a fight to die but not to win."

Speaking at the launching of the submarine Baton Rouge, three months after he had been deposed as Armed Services chairman, Mr. Hebert called himself "the most hawkish of hawks," and termed that year's Congress "the most anti-militaristic, anti-defense and anti-national security" of any in which he had served.

Although Mr. Hebert had his critics and detractors, many were surprised that he was one of the first victims of the House revolt against the seniority system. Only about two dozen persons have ever served longer in Congress. Although some considered him arbitrary, even critics praised him for his courtesy and fairness.

Late in his career, Mr. Hebert himself confided to close associates that he did not truly consider himself a politician. "I'm an old reporter on a long sabbatical," he said.

Survivors include his wife, Gladys, a daughter and four grandchildren.