Beirut — The marine, blond and beardless, and battered by the news that eight more comrades were dead, muttered: ''We're damned if we do fight back, and we're damned if we don't.''
He is one of many people - American and Arab, official or not - asking persistent questions here about the United States military role in Lebanon, after the Americans' unprecedented head-on confrontation with Syrian troops Sunday.
By late Monday, Western news agencies were quoting a statement by Syria's defense minister that suggested such questions may not long be deferred by Washington. The minister, Gen. Mustafa Tlas, was reported as saying in Damascus that a US pilot captured in the air attack would be handed back ''only when the war (in Lebanon) is over. That is, when the Americans will leave Lebanon.''
Some 40,000 Syrian troops have been in neighboring Lebanon since intervening in late 1976 to quell 18 months of civil strife. The US says they, along with Israeli troops who invaded last year, must leave.
About two dozen US jets from offshore carriers in the Mediterranean bore down on Syrian positions in the hill country inland from Beirut Sunday. President Reagan said the attack, the first use of US air power since the start of the American military presence here 15 months ago, was in reprisal for the Syrians' antiaircraft fire on reconnaissance jets the day before.
Two planes were lost to groundfire in the reprisal attack. A US pilot was captured by the Syrians. Another died of injuries. And hours later came the fiercest rocket, mortar, and machine-gun barrage to date against the main US Marine encampment, near Beirut airport - apparently from Syrian-allied Lebanese militiamen in the hills above the airport.
Eight US soldiers died in that firing. Two others were injured. This was the marines' highest one-day death toll since arriving in Beirut, except for October's huge suicide-bomb attack which killed 239 US servicemen.
For the Syrians, the day's outcome seemed something akin to victory - even if the US planes turn out to have wreaked maximum damage on Syrian targets.
Newspapers here and in the US Monday printed a picture showing evidently elated Syrian soldiers next to their downed US jet. It was noted here that US jets had not been lost in combat since the Vietnam war. And over Lebanon, Israel lost only two jets during the entirety of last year's war.
''The Americans have got to look carefully at Lebanon, the traps and labyrinths, and decide what the precise US aims and roles are going to be,'' said one local political commentator privately Monday. In various words, other Lebanese - even the most pro-American and anti-Syrian - said much the same thing.
Some questions involved merely technical matters, likely to be elucidated only in Washington: Why did the US use so many planes, some of them of 1960s design, in the raid? And why were two of them lost?
One Beirut newspaper articulated another question: Were Soviet personnel perhaps manning Syrian antiair positions, making Syrian ''missiles suddenly more accurate''? But at least as persistent were political questions raised here.
Lebanese political analysts of various persuasions argued that the US action - and the subsequent shelling of the bunker-bound Marine force - suggested Washington must urgently come to a clearer idea of what its military presence here is meant to accomplish.
The local analysts, like the young blond marine, suggested this could involve a Hobson's choice.
Mr. Reagan has indicated he means to take a tougher line of reprisal against the Syrians, but still limit US forces to a defensive mandate. Various Arab analysts here suggested this could risk inviting a more assertive line from a Syrian regime that knows it is under less public or political pressure than a US president in election season.
Damascus' Soviet allies are seen as likely to make clear to Syria that any full-scale confrontation with Washington must be avoided. But there is potentially much leeway for trouble, even within such a limit.
Yet as one prominent political commentator added, ''A more fundamental change in US role - involving, for instance, a concerted effort to drive the Syrians out - could, even if it achieved desired effect, involve large casualties, as well as complex political fallout.''