By BILL CARTER

einfeld,'' the most popular television comedy of the 1990's and the centerpiece of the most profitable night in television history, will stop production at the end of this season, Jerry Seinfeld, the show's creator and star, said yesterday.

''I wanted to end the show on the same kind of peak we've been doing it on for years,'' said Mr. Seinfeld. ''I wanted the end to be from a point of strength. I wanted the end to be graceful.''

The loss of ''Seinfeld,'' which made the country laugh at the soup Nazi, close-talkers, chip double-dippers and loaves of marble rye, is a serious blow to NBC, which has already seen its prime-time strength begin to weaken this season.

The show has anchored NBC's big Thursday night since 1993, leading the network to its No. 1 position and to record-making profits, approaching $1 billion this year. ''Seinfeld'' alone has made more than $200 million a year in profits for NBC, according to advertising industry estimates. No other network even tried to put another comedy against ''Seinfeld,'' which has become a cultural signpost in a class with ''I Love Lucy'' and ''The Honeymooners.''

NBC itself considered the show so important that in trying to persuade Mr. Seinfeld to stay, it offered him what one executive said was the most lucrative deal ever extended to a television star.

With the departure of the show, the balance of power in the competition for supremacy during prime time may well shift.

In a statement, NBC said: ''To keep a show of this caliber at its peak has been a great undertaking. We respect Jerry's decision that at the end of this season it's time to move on.''

An NBC official who spoke only on the condition of anonymity said the network would not try to dissuade Mr. Seinfeld by making further offers.

The long-anticipated decision to end the show was Mr. Seinfeld's. The comedian, who is both the show's star and its main creative force, said he decided late Tuesday to wrap up production with a finale episode in May. The remaining episodes will be geared toward that finale.

''We've all seen a million athletes where you say, 'I wish they didn't do those last two years,' '' said Mr. Seinfeld. ''For me, this is all about timing. My life is all about timing. As a comedian, my sense of timing is everything.''

The half-hour show revolves around four single, slightly neurotic and self-absorbed friends who negotiate the perils of love and life in New York City. The characters are Jerry Seinfeld, who plays himself as a stand-up comedian; Elaine Benes, his former girlfriend; George Costanza, his high-school buddy who has trouble keeping jobs, and Kramer, his eccentric neighbor.

Some media critics have said this year's episodes fell short of the show's highest standards, but Mr. Seinfeld maintained that he was not quitting because of those comments. ''We have been very proud of the quality of the work we've done this season,'' Mr. Seinfeld said.

''Seinfeld,'' now in its ninth season, remains the top-rated comedy in television this season, second only in overall rating to the NBC drama ''E.R.'' But for the past full year, counting the repeats, ''Seinfeld'' has been the most watched show ever. As reruns, the comedy is also the highest-rated syndicated series in television, and is expected to make almost $1 billion in syndication revenues.

Mr. Seinfeld's decision came after long and emotional discussions with his co-stars and production staff, and after intense negotiations with executives from NBC. Mr. Seinfeld's associates said the network offered a deal that would have been the richest in television history if Mr. Seinfeld had agreed to continue the show for just one more year.

''It was an extremely difficult thing to do. This show has been the greatest love affair of my life,'' Mr. Seinfeld said. ''But we were all together on it. We all felt we wanted to leave in love.''

One executive familiar with the negotiations, speaking on the condition of anonymity, said Mr. Seinfeld was ''walking away from more money than has ever been offered before to a television star.''

The executive estimated that NBC, led in the negotiations by Robert C. Wright, the network's president, and John F. Welch, the chairman and chief executive of General Electric, NBC's parent company, had offered Mr. Seinfeld about $5 million an episode to stay in production. ''Seinfeld'' produces 22 episodes a season.

''They did everything humanly possible,'' Mr. Seinfeld said, ''but money was not a factor at all. I was not even looking for a raise.''

Some reports have set Mr. Seinfeld's salary at $1 million an episode, but the executive said Mr. Seinfeld was at that figure three years ago. Mr. Seinfeld also profits from the syndication of his series. Forbes magazine put his income for last year at $94 million.

But Mr. Seinfeld said his decision did not hinge on money. Instead, he wanted to follow the tradition of stand-up comedians and leave the stage with the audience wanting more.

His immediate career plans involve a return to his roots in stand-up comedy. Mr. Seinfeld had already agreed to perform a one-man comedy special for HBO next August. He is calling that special ''Laid to Rest,'' and he plans to use material from his stand-up comedy act one last time.

The circumstances of the negotiations between NBC and Mr. Seinfeld were unusual because the decision about whether to continue the series rested entirely with Mr. Seinfeld, who runs both the writing and production staff. He took over sole control of those functions after the 1996 season when his partner, Larry David, who had created the series with him, quit.

Other than Mr. Seinfeld, the rest of the show's ensemble -- Julia Louis-Dreyfus (Elaine), Jason Alexander (George) and Michael Richards (Kramer) -- had already agreed to terms for another season after some acrimonious discussions last spring led to a settlement that is paying them each a record $600,000 for each episode this season.

The show's departure will force NBC to make difficult decisions. First, it must find a replacement for the show next fall. The network's next most highly regarded comedy is ''Frasier,'' but that show anchors Tuesday night and NBC would risk hurting that night by moving ''Frasier'' to Thursday.

Also, the network must decide what to do about the rest of its Thursday-night lineup. NBC has been unable to find a companion show to follow ''Seinfeld'' that had similar widespread appeal and acclaim. Industry executives have speculated that without ''Seinfeld'' on Thursday, NBC would be vulnerable.

The network also faces a costly renewal for ''E.R.,'' which is also on Thursday nights and has a contract that expires in May. And though NBC has been in the No. 1 position for three years, ratings for its regular shows have fallen about 10 percent this year. Without ''Seinfeld,'' the drop-off could worsen.

These are tough times for all the networks, which find it increasingly hard to create hit shows. But the other networks should all benefit from the absence of ''Seinfeld.''

The show began on July 5, 1989, as ''The Seinfeld Chronicles.'' Except for Elaine, all the show's characters were in place in that pilot, but Kramer, played by Michael Richards, was called Kessler in the first episode. Kramer was based on a real person with that name, but the name was not used until the show's producers could locate him and get permission to use his name. The next summer, the show aired six more times, and was scheduled to begin as a regular series in January of 1991, but was bumped off the air by the start of the Persian Gulf war. It finally got a regular time slot on Wednesday nights in the 1991-92 season and for the first half of the 1992-93 season, when it became a cult favorite.

In February 1993, when NBC was facing the loss of ''Cheers,'' it moved ''Seinfeld'' to 9:30 P.M. on Thursdays, after ''Cheers,'' and it became a runaway hit. The next season, it moved to 9 P.M. and has dominated that slot ever since.