"Twilight's Last Gleaming," which opens today at several area theaters, is a protracted, dumbfounding stopover in that simplistic, self-righteous melodramatic cuckooland where Hollywood Liberals presume to have their cake and eat it.

It's ostensibly a doomsday suspense thriller about an attempt to blackmail the government by seizing control of a Titan missile installation. But the picture degnerates promptly into a benighted polemic rationalizing acts of nuclear blackmail as long as they're committed by like-minded fanatics. The moviegoing public is expect to sit still for 150 minutes while the moviemakers congratulate themselves for having a monopoly on political virtue and alertying honest Americans to the contemptible deceitfulness of their leaders.

My affection for Burt Lancaster goes way back, but his insistence on lending himself to such dubious Message Movies as "Gleaming" or "The Cassandra Crossing" or "Execution Action" has begun to be a strain. As an actor, Lancaster contributed a dis- tinctive portrait of polical fanaticism in "Seven Days in May." He hasn't clarified the basic personality by continuing to tinker with it in less proficient and respectable political thrillers. In "Gleaming" he arrives at a dead end, playing a dangerous fanatic whom we're then encouraged to respect as a "modern Messiah," to quote screenwriters Ronald M. Cohen and Edward Huebsch.

The Lancaster character is a former general called Lawrence Dell, who insist that the President, Charles Durning, "level" with the American people. SPecifically, he demands that the President publish a secret document that will alleged ly prove the American government realized from the beginning that intervention in Vietnam would be both futile and destructive and decided to intervene solely "to demonstrate a brutal sense of purpose to the Russians."

Cohen and Huebsch, described as "Political activists" in the press kit, which then spoils the illusion by naming their previous contributions to the literature of the screen-the flop Westerns "Blue" and "The Good Guys and the Bad Guys"-appear to believe that all controversy surrounding American foreign policy will be resolved once this "document"-a euphemism for their own hypothesis-is broadcast. It's difficult to decide which is shakier, the hypothesis or the guilt-cultivating assumption behind the hypothesis.

Lancaster promises to give back the missile base once Durning has come clean with the electorate, kicked in $20 million in ransom, guaranteed safe conduct out of the country on Air Force One and loaned himself as a hostage. The plot is gerrymandered in such a way that Durning must not only acquiesce but also defer to Lancaster's moral superiority. In one of the most absurdly unhealthy denouements I've ever witnessed, Lancaster and accomplice Paul Winfield hustle Durning back to his plane at gunpoint, and events follow which neatly shift blame back onto the military and government.

The general level of the entertainment may be gauged by such bulesque exchanges as the following, shared by Durning and Richard Widmark, who appears as a sneaky SAC chief:

"Do you mean to tell me a renegrade general has his finger on the button?"

"No, sir, he has control of nine Titan missiles."

"I want to ask a straight question. Is there any chance of talking those bastards out of there without endangering the world?"

"I don't believe so, sir."

I appreciate your candor, Colonel."

"Gleaming" might be a source of mischief if it were crisp, exciting melodrama. But the stilted, widely dialogue and the presumably inadvettent goofiness of much of the action should restrict its appeal in this country to the dwindling number of moviegoers who like to catch everthing, including the stinkers.

It's conceivable that the target audience is, in fact, foreign rather than domestic. Despite its saving-the-Republic pretenses, "Gleaming" was shot in and around the Bavaria Studios in Munich, a delightfully ironic choice of location.

Lorimar, the American partner in this co-production, is branching out for such TV features as "The Homecoming," "Helter Skelter" and "Sybil" and such series as "The Blue Knight," and such series as "The Blue Knight," "Apple's Way" and "Doc Elliott." It takes a curious kind of gall to invite the enmity of domestic movie unions on the one hand and domestic audiences on the other by perpetrating a runaway production that presumes to instruct us in the wickedness of the American government.