A couple of longtime television institutions rode off into the sunset last week - "Dallas" and Brandon Tartikoff.

And like the long-running CBS soap, the chairman of the NBC Entertainment Group had also outlived his usefulness.Tartikoff, who's actually leaving July 1 to become head of Paramount Studios, has been heaped with praise for guiding NBC from last to first place during his 11-year reign. He's been lauded for doing it with quality programming like "Hill Street Blues," "L.A. Law" and "Cheers."

But, in television terms, this is all ancient history. NBC hasn't come up with a hit since "Empty Nest" premiered in 1988. (And you can make the case that "Nest" has only ridden the coattails of NBC's last real new hit, "The Golden Girls," which premiered five years ago.)

And if Tartikoff is going to reap the praise for NBC's programming triumphs, he must shoulder the blame for junk like "Misfits of Science," "Manimal," "Baywatch," "Grand," "The Nutt House," "Ferris Bueller" and "Hull High."

Not to mention the fact that Tartikoff has been getting all the credit for the tone former NBC chairman Grant Tinker set. Part of the Tartikoff legend was his renewal of low-rated shows like "Cheers" and "Hill Street Blues," allowing them the time to build an audience and become big hits.

But it was Tinker who, from 1981-1986, stressed the practice of putting quality shows on the air and allowing them to build an audience.

The relative paucity of NBC success since Tinker left says more about Tartikoff than those early years.

It's not just that NBC has been unable to come up with hit shows in the past few years, the greater failure has been the network's unwillingness to stick with quality shows that don't instantly offer great ratings.

This season alone, excellent shows like "Parenthood" and "Working It Out" were first badly scheduled, then yanked without so much as a second thought.

As a matter of fact, the decline of NBC can be traced back to a similar decision in 1988. Tartikoff canceled the absolutely wonderful show "A Year In the Life" after a single season, driven by apparent paranoia over remaining the No. 1 network instead of giving quality a chance.

(The producers of "A Year" have since gone on to create the equally wonderful "Northern Exposure" - for CBS.)

There were other symptoms during that 1988 season that the Peacock had peaked. Over the objections of NBC News, Tartikoff scheduled Geraldo Rivera's sleazy special about Satanism - a ratings ploy that tarnished the entire network.

In his defense, many of the factors in NBC's decline were beyond Tartikoff's control. When he took over 11 years ago, the networks hadn't yet suffered the inroads that cable, videos and Fox have made in their audience.

The sale of NBC to General Electric put the network at the mercy of a huge, heartless corporation greatly interested in the bottom line but without any knowledge of the broadcasting industry.

And staying No. 1 is a lot harder than becoming No. 1. There's a natural tendency to play it safe, to go for the quick ratings instead of building for the long term.

Not to mention that when your schedule is laden with strong shows, the producers start taking their new programs to the other networks, which have more holes to fill.

Of course, those producers have increasingly turned away from NBC in recent years because of the network's itchy cancellation finger.

NBC insiders have been indicating for several years now that their boss seemed bored with his job. Once you've fought your way to No. 1 and stayed there for six years, what else is there to accomplish?

Tartikoff will go down in television history as a master programmer. He's also a wonderfully personable man who's extremely popular with the press.

But Tartikoff leaves NBC as a network in disarray. The Peacock barely held onto first place in the network race this year, and most analysts believe it will fall off that perch next season.

It can't find a new hit. Its old hits aren't aging gracefully - not only are they losing massive shares of their audience but they're costing NBC a fortune to keep on the air because of higher rights fees.

The network's daytime schedule is a disaster. So is its Saturday morning lineup. The "Today" show is still No. 2, and "The Tonight Show starring Johnny Carson" isn't making the kind of money it once did.

It's already too late for Tartikoff to get out while the getting is good. NBC is still No. 1 in prime time - barely - but it's clearly on a downward trend.

But it will be Tartikoff's handpicked successor, Warren Littlefield, who'll shoulder most of the blame.