On a day when NBC's Jay Leno and Conan O'Brien dealt a blow to striking film and television writers by announcing that they would cross the picket line to go back on the air -- and ABC's Jimmy Kimmel prepared to do the same -- the Writers Guild of America flexed its own muscles by denying waivers to the producers of the Golden Globes and the Oscars.

The decision means that Dick Clark Productions and the Foreign Press Assn. will not be able to employ writers to craft the script for the Globes, which airs Jan. 13 on NBC, and the Academy of Motion Picture Arts and Sciences will not be allowed to show clips of movies and past award shows in the February telecast of the Oscars without paying residuals for their use.

People close to the guild's board said the union also decided it would not permit writers to work on the Oscars, although the academy has not asked for such a waiver.

The WGA's stance essentially makes the high-gloss awards shows "struck productions." As such they probably would be boycotted by Hollywood's A-list writers and the actors sympathetic to their cause. The WGA said Monday that it was too early to discuss picketing plans. The move underscores the tensions between the guild and the major studios, which typically enjoy major promotional pushes from the telecasts.

In letters sent Monday night to the producers, Patric M. Verrone, president of WGA West, said the union decided that granting their requests would not help the guild's position in the 6-week-old strike.

"We must do everything we can to bring our negotiations to a swift and fair conclusion for the benefit of writers and all those who are being harmed by the companies' failure to engage in serious negotiations," Verrone wrote. "Our board concluded, reluctantly, that granting a waiver . . . would not advance that goal."

Bruce Davis, executive director of the academy, said he was taken aback by the WGA's refusal to grant the organization a waiver to use the film clips. The academy was planning to wait to make its request for a writing waiver for host Jon Stewart and his writing staff after "the dust settles," an effort that now appears futile.

"This is striking more at the heart of what we do," Davis said.

In a statement, Dick Clark Productions expressed its disappointment that its request was denied but said it hoped to work out a separate deal with the WGA so it could employ writers for the Globes.

The union's decision about the awards programs came on the heels of NBC's announcement that Leno and O'Brien would go back on the air Jan. 2. ABC plans to announce today that host Kimmel will return to the air the same night, according to a source familiar with the discussions.

The NBC comedians, who are both WGA members, said they supported their writing staff but must return to work to save the jobs of hundreds of others who work on the shows. Since NBC laid off the production crews at the end of November, Leno and O'Brien have been paying the salaries of their staff members themselves, a significant expenditure they appeared unwilling to shoulder indefinitely.

"Now that the talks have broken down and there are no further negotiations scheduled, I feel it's my responsibility to get my 100 non-writing staff, which were laid off, back to work," Leno said in a statement. "We fully support our writers, and I think they understand my decision."

O'Brien, who described himself as an "ardent supporter" of the guild, said in a separate statement that he had to decide whether to "go back to work and keep my staff employed or stay dark and allow 80 people, many of whom have worked for me for 14 years, to lose their jobs."

The decision by the NBC hosts to return to the air after their shows languished in reruns for six weeks marks a sobering turn for the union, which last month trumpeted Leno's appearance on the picket line as evidence of the high-profile support for the writers' cause.

NBC's Carson Daly, who is not a WGA member, had been the only late-night host to resume production in late November, a move that drew derision from many writers. The guild also lambasted Ellen DeGeneres last month when she resumed taping her syndicated daytime talk show.

The union's response to the decision by Leno and O'Brien seemed muted by comparison.

"NBC forcing Jay Leno and Conan O'Brien back on the air without writers is not going to provide the quality entertainment that the public deserves," the guild said in a statement.

Similarly, the shows' own writers took pains not to criticize Leno or O'Brien, whose personal payments to their staffs earned them substantial goodwill.

"We knew it was just a matter of time before late night would come back," said Joe Medeiros, head writer for "The Tonight Show With Jay Leno," as he picketed outside NBC's Burbank headquarters. "But Jay has been very supportive to us, and we support him."