Philip C. Habib and Morris Draper, who are stepping aside after two years in a diplomatic assignment that has become a metaphor for frustration, were often seen but rarely heard as they strode past the cameras at each stop of their endless Middle Eastern tour.

Habib, the rough, gruff son of Lebanese immigrants who has twice come out of retirement at the behest of two presidents, acquired a reputation for tough-talking candor behind closed doors and stoic silence outside them.

He is leaving what many describe as the toughest diplomatic assignment in the world as quietly as he entered it, with extraordinary praise from his colleagues and some significant successes, but at a time when progress in the decades-old regional conflict seems again to have ground to a halt.

The veteran Brooklyn-born negotiator has made a career of taking on the most intractable foreign policy problems, where the stakes are high and progress comes--if at all--in slow, tiny steps.

In a career spanning three decades and every president since Eisenhower, Habib, 63, first came to prominence as head of the American delegation to Paris in 1969 and 1970, attempting without success to prod the North Vietnamese into starting "serious discussions" at the peace table.

Now retiring for the third time, Habib leaves the foreign service with "the shredding of Lebanon," as he has described it, as yet unrepaired.

But colleagues said yesterday that success is measured in relative terms in places like Vietnam and Lebanon.

Habib and Draper, in their own eyes, probably had their greatest accomplishment in an 11-month cease-fire, from July, 1981, to June, 1982, between two bitter enemies--Israel and the Palestine Liberation Organization--who would not officially recognize each other's existence.

Then last summer, with Israeli troops poised outside Beirut and PLO and Syrian fighters dug in within, the two veteran negotiators averted street-to-street bloodshed by arranging the withdrawal of the Palestinians and their allies.

"Last summer there were only two people who thought that Phil and Morris could get the Syrians out of Beirut, and that was Phil and Morris," a source close to the talks said. "So you don't give up."

Habib's and Draper's latest accomplishment in the region came May 17, when Israel and Lebanon signed an agreement intended to begin the withdrawal of foreign troops from Lebanon. But the agreement turns on Syria's willingness to withdraw as well, which it has shown little inclination to do.

Friends and associates say that the strain of his long and grueling Mid East tour has taken its toll on Habib, who suffered a heart attack that nearly killed him in 1975. He has had major surgery for the condition at least twice.

"I have the highest regard for the foreign service, but Phil is a rare bird," said former secretary of state Cyrus R. Vance, who called Habib back from private life the first time, in 1976. "He's got everything you're looking for in a foreign service officer: He'll tell it to you absolutely straight, won't hesitate to tell you when you're wrong, and he's got good judgment and a lot of imagination."

Henry A. Kissinger, Vance's predecessor, once wrote that Habib "was the antithesis of the public stereotype of the elegant, excessively genteel foreign service officer. He was rough, blunt, direct, as far from the 'striped pants' image as it is possible to be."

The son of Lebanese Maronite grocers, who raised Habib in the predominantly Jewish Bensonhurst section of Brooklyn, Habib rose to the rank of captain in the U.S. Army during World War II and later completed course work for a doctorate in economics at the University of California at Berkeley before joining the State Department in 1949.

Vance asked Habib to return to Washington after his first retirement to help craft policy toward Cuba and the Caribbean. In May, 1981, President Reagan pulled him out of retirement again for his current Middle East assignment.

Draper, also a career foreign service officer, has served as Habib's deputy and has handled many of the day-to-day details of shuttle diplomacy. A Phi Beta Kappa graduate of the University of California, Draper, 55, is fluent in Arabic and French and is considered knowledgeable about the Arab world.

He has served for two decades almost entirely in the Middle East.

Habib and Draper were followed from office yesterday by an outpouring of praise from colleagues in the White House and on Capitol Hill.

Reagan said that Habib "will be sorely missed." Robert C. McFarlane, who is replacing Habib, called him "a giant." Secretary of State George P. Schultz described him at his Senate confirmation hearings a year ago as "a real hero."