With music striving in the background, a bare-chested boy of 11 creeps under barbed wire barriers. Submachine-gun bursts kick up dust beside him as the camera closes on his face, which is twisted with effort and concentration. Suddenly the film stops to freeze the image of the littlest commando, training for war before he grows a beard.

The full-screen portrait is perhaps the most compelling moment in ABC's hour-long look at the Palestinian guerrilla movement tonight at 8 on Channel 7. The program, "Terror in the Promised Land," gives a rare sympathetic look at the plight of the Palestinians and what propels their young men into guerrilla ranks.

The documentary, produced and directed by Malcom Clark, is likely to generate criticism from the broad category of Americans, Jewish and non-Jewish, who are used to viewing Palestinian commandos as President Carter seems to - in a class with Nazis, Communists and Ku Klux Klan cross-burners. But then many may not be watching; opposite the examination of the Palestinian cause is CBS' examination of Charlie Brown, the Great Pumpkin and Puff the Magic Dragon.

"Terror in the Promised Land" is not kid stuff. Correspondent Frank Reynolds warns in his opening that parental discretion is advised, presumably because of raw footage showing mass burial of Jewish concentration camp victims.

The horror scenes were judged necessary to pound home the suffering of the Jewish people during World War II, which precipitated the large-scale immigration to Palestine and led in turn to the suffering of the Palestinian people. The resultant conflict is summed up in a neat and unusually candid manner for the ABC camera by Rannon Weitz, director of the Jewish National Fund that is responsible for settling Jews on formerly Arab land.

"We used Arad land for our survival," he says. "And the problem and the issue is a clash between two justices. And the answer for such a situation is a painful compromise. There is no escape from that."

The subject of "Terror in the Promised Land" is the Palestinians who feel all the compromises so far have been Israeli victories, and that the only effective way to return to the land where they or their fathers were born is to win it with a rifle. Or a terror bomb in a marketplace. Or a Jewish hostage in a kibbutz. Or whatever works.

Long sequences are devoted to explanations by commandos in southern Lebanon training for cross-border suicide mission, telling the camera why they are ready to take their own lives and those of civilians during raids into Israel. Despite their cant, the viewer finds it difficult to see evil in the eyes of a young man declaring his readiness to die for an ideal.

"This program is not about right and wrong," says Reynolds at the outset. "It is about the Palestinian perception of right and wrong."

In a sense, it also is about American perceptions of the Palestinians. As Reynolds remarks, the guerrilla leaders often complain their story is not told accurately in this country.

The ABC program clearly is an attempt to do so, without judging the rights or wrongs of the case. To the extent that it leaves aside the accusatory tone that marks so much reporting on the Palestinian guerrilla movement, it seems to succeed. But viewed in another light, the program itself is an illustration of why the complaint is made.

Terror is the subject. But the program focuses on military training of uniformed commandos within the regular guerrilla structure under Abu Jihad, military commander of Yasser Arafat's Fatah group. Little attention is given to the shadow world of Palestinian leaders who have made a trade of the ugliest terror, aimed at civilians far from the Middle East battlefields. People like Wadia Haddad, who until his reported death last year carried on th eairline hijacking tradition long after it was abandoned as useless by its inventor, Dr. George Habash of the Popular Front for the Liberation of Palestine; or Abu Nidal, a Baghdad-based plotter who is such an extremist that Arafat has put a price on his head.

The distinction seems worth drawing.

We are, however, offered what Reynolds calls a "rare glimpse" of Abu Hassan, chief of Fatah security and reputedly the chief Black September planner of the Munich Olympics operation in 1972. It didn't seem so rare to those who shared the bar with him during his nocturnal prowls around Beirut in the Lebanese civil war.

Abu Hassan, whose real name is Ali Hassan Salameh, was one of the top targets on the hit list of an Israeli assassination team dispatched to seek revenge after the Munich massacre. The ABC program lists 10 of its Palestinian victims one by one, with their deaths attributed to Israeli killers on the faith of "intelligence sources" in an unusual effort to show that terror in the Middle East is two-way.

The sequence, which the producers said followed considerable thought and discussion, is treated like a revelation. Actually, the assassinations were the subject of a book published two years ago by former Time magazine correspondent David B. Tinnin entitled "The Hit Team."