"Fly Away Home" quickly gets itself nose-deep in the wrong Big Muddy. Stirling Silliphant's film about the Vietnam war was supposed to have been a year-long ABC series, but the network, perhaps after seeing tonight's haphazard two-hour movie version, canceled the project. As rarely occurs in television, one's tendency in this case is to side with the executives; "Fly Away Home" is writer-producer Silliphant's Big Muddle.

The film, at 9 tonight on Channel 7, opens on the eve of the Tet Offensive, and Silliphant apparently was going to follow the trails of four people caught up in the war: a news cameraman (blank Bruce Boxleitner), a surly soldier (Michael Beck), a young black man who enlists after his brother dies in the war (Randy Frederick Brooks) and a beautiful Vietnamese woman doctor who agonizes at the drop of a hat about the fate befalling her country (Tiana Alexandra, who happens to be Mrs. Silliphant).

But the film totters out of the starting gate and spends the rest of its time teetering. We know we're in trouble when the black soldier, who has been assigned the rib-ticklingly poetic first name of "Shenandoah," has a static confrontation with his mother, played by Olivia Cole, who doesn't want him to go to Vietnam. They heave stares and sighs at one another for what seems like half an hour; the scene is an anvil in the audience's lap.

Then the soldier himself goes to Vietnam and completely disappears from the screenplay. Apparently his fate was to be detailed in a future episode.

In Vietnam, Boxleitner encounters Brian Dennehy as a macho-cynic news producer who fills him in on the real skinny, a tedious succession of neuter truisms. Meanwhile, the Vietnamese woman discovers her parents, a military official and a Madame Nhu-type mommy-dearest, are skimming funds from the soldier boys, and when she presents this information to mom, the woman scoffs at her naivete' and asks, "How do you think you were able to have such a nice apartment in Paris?"

The young woman enlists as a doctor, but even during the tumult of battle finds time to rail against seas of troubles. Told by U.S. military men that she has just 30 more minutes to treat wounded children, she ominously responds, "Colonel, 30 minutes has very little meaning in a war we've been fighting for more than a century." This is some heavy trip, all right, but not one worth taking.

On tonight's edition of "NBC Magazine With David Brinkley" (on Channel 4 at 8) -- Brinkley's last program and his last broadcast for NBC News -- the master communicator ambles through a sprightly profile of Barry Goldwater at 72 that is inadequate to its subject but highly rewarding just the same.

Goldwater's once ridiculed notions became "accepted by most in 1980," says Brinkley -- an arguable thesis -- and he has become, in the cantankerous candor of his 70s, a hero to many who may once have feared him. Looking back on his early '60s image and such mementos as Tony Schwartz's famous anti-Goldwater "daisy" commercial (the little girl and the A-bomb), the 1964 Republican presidential candidate growls, "If I had known Goldwater, I'd have voted against the S.O.B."

The footage of Goldwater today is so good and the man such an ingratiating roughneck and iconoclast that the report seems much too short, but what there is, to quote Spencer Tracy, is cherce. It shouldn't be lost on anyone that Brinkley, like Goldwater, is a tough cookie who likes to get his own way and speak his own mind; they are cherishable curmudgeons, both of them.