The freedom to avoid ponderous three-hour network encyclicals is a precious one. Viewers can exercise it with impunity when it comes to "The Blessings of Liberty," a three-hour ABC News report on the 200th birthday of the Constitution. Insufferably lengthy and, worse, arduous, the program rehashes much of ABC's three-hour 1985 documentary "45/85."

That program, justifiably acclaimed, had a relatively tight focus; it both summed up and summoned up 40 years in American political and social history. "Blessings of Liberty," tonight at 8 on Channel 7, recycles similar material in an attempt to sweeten and lighten an examination of landmark Supreme Court cases and constitutional amendments.

Despite, or because of, all the bangety-clang and firecracker kinetics, the show doesn't work. It seems more an inundation than a celebration. There's so much stock footage that watching "Liberty" is like being trapped overnight in a film library.

David Brinkley, Peter Jennings and Ted Koppel trianchor the report, speaking stiffly as they strut about the rotunda of the National Archives. During the on-camera narration, they repeatedly hand off rhetorical batons to one another, doing the shim-sham and the hokey-pokey across the rotunda floor. One begins to wonder why no choreographer is listed in the credits.

Jennings does his suave routine, looking as though he should be sipping cognac and occasionally bringing Roger Moore to mind. Koppel orates in loudest pontificalese; he was born more to ask than to declaim. And Brinkley looks elegantly mortified about just having to be there, as if he'd rather be sitting in a dentist's chair or under a sunlamp in Death Valley.

Even if he wrote them himself, Brinkley can't have been comfortable making such tritely trifling social observations as, during a look at the 1960s, "Hemlines were up, and so was the surf."

The producers were determined to keep a multimedia whirlwind spinning. There are chalk drawings, old newsreels, still photos, scenes from Hollywood movies (sometimes, as is a new tradition in TV news, not identified as such), film clips from "The Adams Chronicles," archival bric-a-brac and historical sound bites by actors playing important personages: Cicely Tyson as Sojourner Truth, E.G. Marshall as William O. Douglas, Roy Scheider in a scene from "Babbitt," Richard Kiley as George Washington, Louis Gossett Jr. as Frederick Douglass, and so on.

These interludes are poorly shot and directed (the Scheider scene begins with studied contemplation of a chair) and most grievously overemoted. F. Murray Abraham as Patrick Henry is sheer torture.

But the producers have daffier tricks up their sleeves. In the third hour, shots of the locked gate at an abandoned Lockheed plant are accompanied by the song "Don't It Make My Brown Eyes Blue," and an empty factory in Maine is inscrutably serenaded with the old Bread ballad "If." The program seems as pantingly anxious to amuse as a fun-house ride at Disneyland.

In truth, that final hour contains formidable, worthy, compelling material, dealing with constitutional issues still being fiercely debated -- at the Robert Bork confirmation hearings, among other places. But most of what's in the preceding two hours is expendable and windy, as doggedly routine as a small-town politician's Constitution Day speech. Jennings, Koppel and especially Brinkley are demeaned by it.

There's one slightly catty moment, too. During a sequence on civil rights, Fred Graham appears briefly and is identified as a "former New York Times reporter" -- which ignores Graham's more recent, 14-year career at CBS News. Perhaps this was Graham's choice. He was a victim of one of CBS President Laurence Tisch's search-and-destroy missions and is now a local anchor in Nashville.

Minor quibbles aside, "Liberty" is a major disappointment. Just before each commercial break, one of the three anchors begins a tease by saying, "When we come back ..." Only three or four of these go by before a reasonably patient viewer feels tempted to respond, "Oh, must you?"

CBS Crimes Prime-time television has become a crash course in criminology and, from a network executive's point of view, the more crashes, the better. CBS has two new cop shows getting on-air "previews" tonight -- "The Oldest Rookie" and "Wiseguy" -- and both are CBS specialties: crashing bores.

In "Oldest Rookie," Paul Sorvino plays a chubby police department public relations man who decides, after 25 years on the force, and upon the death of a close friend, to become a regulation street cop, although he soon tires of that and gets his buddy the mayor to make him a detective.

His partner is, naturally, a brash young cop (D.W. Moffett), one who has a basketball court in his spacious loft apartment, which suggests that in this city, police work pays well. The two go through rudimentary cop-show scrapes and the producers let the tires squeal where they may. The chief is set up as a stock nemesis, so vicious and nasty that a month of Ann Landers columns couldn't straighten him out.

Something might be able to straighten out "The Oldest Rookie," but nothing would be worth the trouble.

"Wiseguy," which gets a two-hour inaugural at 9 on Channel 9, deposits blank-faced lump Ken Wahl onto the screen for a preposterous and desultory crime saga about a sullen undercover cop who infiltrates the mob and will spend each episode almost getting found out, but miraculously squeaking through.

Wahl, a dead (used advisedly) ringer for "Houston Knights" star Michael Pare', graduated from the academy of thespic subminimalism. Anything more than showing up on the set would apparently be a stretch for him. Ray Sharkey, a volatile and underused actor, is stuck with the part of the mob boss who, in a ridiculous pseudo-macho encounter, takes a shine to the young lad after being insulted by him at a restaurant and pummeled by him in a manly fistfight.

Inducted into the underworld fraternity, Wahl is given his own Porsche, the car of the year in TV crime circles (Margaret Colin drives one on "Leg Work," also on CBS). Some of the cops in "Wiseguy" appear to be as corrupt as the hoods are, though they are much less stylishly dressed and don't have Porsches. The implication is troubling, but would be more so if the life expectancy of "Wiseguy" didn't look to be one or two months at the most.

That will be one or two months too many.