As autumn's last brown leaves quivered in an icy wind, the 20-year-old Marine corporal killed defending the U.S. Embassy in Pakistan was buried yesterday afternoon on an Arlington hillside.

Although the ceremonies offered all the pomp the military can provide, the services for Steven J. Crowley, who joined the Marines immediately after his high school graduation, lacked the finality that accompanies most funerals.

The president and a host of dignitaries came to the burial at Arlington National Cemetery -- an event that spotlighted the tensions of the Pakistan crisis just past and the continuing Iranian crisis.

The president, looking haggard, entered the octagonal, eclectically modern chapel on the nearby Fort Myer base with Crowley's mother Georgene leaning on his arm. Behind them were Crowley's brothers and sister -- eight in number -- a picture of solemnity under the harsh sun pouring in through the windows.

The presence of Secretary of State Cyrus Vance, Secretary of Defense Harold Brown and New York Sens. Daniel P. Moynihan and Jacob Javits also lent an air of gravity, of high state urgency to the rites.

The ceremony itself emphasized Crowley's extreme youth. "For one who dies at the age of 20 . . . there is not much time," said Navy chaplain Lawrence J. Finegan, the celebrant of the hour-long funeral mass.

Rep. William Carney, who represents the Crowley family's Port Jefferson, N.Y., hometown, read a letter to the assembly which he said was typical of the thousands the family had received.

The letter writer said that what he had read about Crowley's death defending the embassy in Islamabad from Moslem rioters, had made him cry, "My God, he was just a kid," the man wrote, adding, "I'm only twenty-two and a half myself."

"It's become so hip, so cool . . . to meanmouth the country," the writer continued. It's refreshing to read that Steve had the guts to be different." c

Carter did not speak during the course of the service. He spent much of it with his eyes closed, his face conveying an attitude of intense prayer.

Even as Crowley's life was remembered, it was hard for the congregation to forget the events that had magnified his death.

The Most Rev. John J. O'Connor, a former chief of Navy chaplains and now a bishop with responsibilities for the armed forces, sought to break the tension among those in the chapel, many of whom had worked in the embassy with the young Marine.

"There's only one real dignitary here right now and that's Steve," said O'Connor, looking directly at Carter. He then led a long round of applause for Crowley.

O'Connor then described the Crowley family as "simple folks," and attributed to their next-door-neighbor a brief epitaph for the serviceman:

"We lost a little piece of America . . . but maybe we have again the spirit of America."

The Catholic bishop then urged the crowd into a second round of applause for the neighbor's words "in hopes that it will give our president . . . strength and courage.

"Instead of customary prayers, let us pray as we have never prayed before," O'Connor concluded.

Crowley was killed Nov. 21 when the American Embassy in Islamabad was attacked by angrey demonstrators, who had heard erroneous reports that the United States was responsible for a siege then in proress at the Great Mosquie in Mecca, the holiest shrine n the Islamic world.

During the attack, Crowley remained at an exposed location on the roof providing information on the scene outside the embassy, as Americans withdrew to the security vault in the embassy compound.

For his bravery, Crowley was posthumously decorated with the Bronze Star and the Purple Heart. His actions "reflected great credit upon himself and upheld the highest traditions of the Marine Corps . . .," said a citation accompanying the awards.

After communion and the singing of the Navy Hymn, Crowley's flag-draped casket was carried from the chapel with Carter, Mrs. Crowley and a retinue of dignitaries and Marines in close attendance.

Minutes later, the cortege, minus Carter, assembled again inside Arlington Cemetery under a cloudless sky.

A volley of rifle shots pierced the chilly air. Taps were played. Secretary of State Cyrus Vance approached Mrs. Crowley to offer a few words.

And that was all. With nothing else left to do, the crowd of 1,000 mourners slowly retreated from the gravesite, leaving Steven Crowley to his final rest.