Lt. Col. Domingo Monterrosa, El Salvador's top Army field commander until his death Tuesday in a helicopter crash, was buried here today in a solemn and emotional ceremony.

Monterrosa's interment in the capital's general cemetery this morning was an event without precedent in the five years of civil war in which more than 40,000 people have been killed.

President Jose Napoleon Duarte and his whole military high command turned out to pay their respects to a man who had been billed as the bright hope of El Salvador's long-criticized Army. In doing so they turned the ceremony into the first full state funeral held here in years.

"You are a hero, a national hero," said the colonel's military academy classmate, Col. Roberto Rodriguez Murcia, in a eulogy under a hot sun and a blue sky before Monterrosa's open grave. "You have set an example of courage, honesty and integrity to all the armed forces, and your spirit will carry on in our hearts, and we will follow in your footsteps."

As a lone bugler standing on a nearby tomb in the crowded cemetery blew taps, some in the crowd chanted, "Viva the people's martyr" and "Vivan the soldiers who have fallen for the nation."

The blue and white Salvadoran flag that had draped the burnished aluminum coffin on its slow passage through the streets to the cemetery was folded and handed by Defense Minister Carlos Eugenio Vides Casanova to Monterrosa's two sons, Domingo Antonio, 18, and Alvaro Jose, 17, who had flown to the funeral from their home with their mother in San Francisco, Calif.

"Your father has died, but a hero has been born," Vides Casanova told the two boys as tears rolled down their faces. "Remember that those of us who knew him and fought with him will always hold this banner high and let it serve as his final example to you in your future life."

As the coffin was lowered into the grave, the sobs of the hundreds of mourners who had jammed in around it were a reminder of the national shock that Monterrosa's death has produced in the country.

Monterrosa died with 13 others, including three other key field commanders, when his helicopter exploded in the air and crashed to the ground last Tuesday shortly after it had taken off from the town of Joateca in the eastern province of Morazan, where the guerrillas are particularly active and where his units had been conducting an offensive.

An official Air Force investigation conducted at the crash site by a major and a lieutenant officially has backed up earlier military reports that the helicopter crashed because of mechanical failures, officials said today.

The guerrillas' clandestine Radio Venceremos repeatedly has claimed Monterrosa's helicopter was ambushed by rebel machine gunners who had infiltrated into the hill-crests surrounding Joateca. Witnesses interviewed by reporters have described the helicopter exploding in midair, as if hit by hostile fire.

So delighted were the guerrillas at the death of Monterrosa, generally thought to be their most effective opponent, that while President Duarte ordered three days of national mourning, they declared three days of holiday in the zones they control.

Monterrosa's death has stunned the government and the nation because he was considered -- as the overall commander in the country's three eastern provinces -- the man most responsible for the Salvadoran Army's recent success in wresting the initiative from the guerrillas.

Although Duarte and the Army high command have moved quickly to replace the fallen commanders and to insist that nothing will change, Salvadoran and foreign analysts say Monterrosa's death is a serious setback in the war, if nothing else because of its psychological impact on the Army.

A reminder that the war goes on came just before the funeral today when three young men driving in a white car with no license plates drove up behind 62-year-old Raul Menendez Aquino, the head of the U.S. Embassy's local guard force, and shot him dead as he was walking to work.

According to witnesses, the assassins shouted out the window after the shooting, "We are the FPL, and this is an embassy dog." The initials FPL stand for Popular Liberation Forces, one of five guerrilla organizations fighting the government.