LIONEL CHETWYND has achieved the impossible -- making a Vietnam prison torture movie dull. And although his sympathy for Americans missing in action seems genuine and laudable, the film liberal-bashes so heavyhandedly it's enough to make Nixon cry "Fonda."

The film portrays the plight of several American airmen imprisoned and tortured in the Viet Cong Hao Lo prison between 1963 and 1975. It begins with the capture of Lt. Cmdr. Williamson (Michael Moriarty) and ends when the prison is liberated after the inmate ranks have swelled to almost 300.

The "Hanoi" depiction of patriotic Americans ignored by their own country, with only the camaraderie of their cellmates to sustain them, could have made riveting drama. But Chetwynd's characters are as dreary as their cells, and there are so many POWs they become indistinguishable. The multiple casting reduces each character's screen time, so there's no one to really root for.

Frustrated, we flit from cell to cell like a mosquito looking for good blood. When the prisoners are tortured (we see only one torture scene directly) it doesn't seem that tragic. We wince, but we don't empathize. "The Great Escape" this isn't.

Cardboard western liberal journalists (including one unsubtly based on Jane Fonda) come to interview the captives and appear to want only unpatriotic answers that extol the Viet Cong and please their comsymp hearts. And then there's a Cuban officer (name of, er, Fidel) imported to the camp to break the Americans' spirit. He has a thick New York accent because he grew up on 110th Street. Came right out from under an American bed. "Wherever we can kick Yankee (expletive)," he tells an American, "you'll find my people."

Moriarty's Williamson, who becomes the senior ranking officer through attrition, is the most central character. His quiet determination to hold on to dignity comes closest to arousing sympathy, but he gets crowded out. He surfaces and resurfaces but drifts away. And he seems to have difficulty crying.

The other characters are either reduced to one dimension (like the Jesuit-trained camp commandant, who struts before cheap paintings of Mao Tse Tung and Ho Chi Minh, mulling whom to torture next) or they're downright uninteresting. Paul Le Mat, as a recalled Korea veteran who just wants to get home in one piece, and Jeffrey Jones as Major Fisher, who prepares himself for impending death with a growing spiritual strength, show promise. Until Chetwynd's script deserts them.

THE HANOI HILTON (R) -- At area theaters.