Speaker of the House Thomas P. O'Neill Jr. (D-Mass.) stopped in at a Boston bar the other day, only it wasn't in Boston. It was on the lot at Paramount Studios in Hollywood, where O'Neill made his acting debut (unless one counts his appearances on House TV) playing himself in an episode of the NBC comedy series "Cheers."

O'Neill's cameo appearnace in the series, which is set in a Boston bar, will be the "teaser" opening scene on an episode to be seen "in a couple of week," according to a Paramount spokesman who said a definite air date has yet to be set.

In the scene, O'Neill is seated at the bar and approached by a waitress played by series regular Rhea Perlman, who says to him, "Hey, you look like Tip O'Neill," to which O'Neill responds, "I've heard that, but I'm much handsomer."

O'Neill's favorite character on the program is a tubby barfly named Norm (George Wendt) who, in the scene filmed Monday, complains loudly about the "bozos" on Capitol Hill, sits next to O'Neill, and says, "This bozo next to me could do just as well as those guys in Congress." He asks O'Neill where he works. O'Neill says "the House." Norm thinks this means O'Neill stays home while his wife works.O'Neill says, "No, I'm the speaker of the House of Representatives."

Norm says, "Well if you're the speaker of the House, I'm a horse's butt."

Tip says, "You said it; I didn't."

The filming came about because the casting director of "Cheers," Steve Kolzak, 29, is the son of Dolores Snow, who worked for 15 years as an assistant to O'Neill and is now assistant to the clerk of the House. Snow said yesterday that she recommended O'Neill watch the show over the holidays, and after he took her advice, told her he'd gotten "a big chuckle out of it" and then began to imagine himself at the bar trading quips with Norm.

Kolzak contact O'Neill and the speaker agreed to appear while in Los Angeles on his way to the Bob Hope Desert Golf Classic in Palm Springs. "Cheers" has languished at the bottom of the ratings throughout the TV season, but a Paramount spokesman said that in recent weeks there has been "a little movement," up, for the Thursday night comedy. He also said O'Neill is donating the fee for his appearnace to the Cambridge (Mass.) Boys Clubs.