US film and television writers started going on strike on Monday as last-minute talks aimed at averting the Writers Guild of America's first strike in almost two decades collapsed, the union said.

The strike is expected to shut down many sitcoms and send popular late-night talk shows such as NBC's "The Tonight Show With Jay Leno" and CBS' "Late Show With David Letterman," immediately into reruns as they rely on a stream of topical jokes.

The members of the union's East Coast arm officially went on strike at the designated deadline of 12:01 a.m. EST (0501 GMT). Their West Coast counterparts were set to follow them three hours later.

The East Coast walkout led to the collapse of 10 hours of talks in Los Angeles between the union and the Alliance of Motion Picture and Television Producers (AMPTP), which represents the studios.

The two sides have been mired in contract negotiations for months, but hit an impasse primarily over demands by writers for higher fees, or "residuals," derived from the sale of movies and TV programs on DVDs and the Internet.

"Notwithstanding the fact that negotiations were ongoing, the WGA decided to start their strike in New York," AMPTP president Nick Counter said in a statement.

"When we asked if they would 'stop the clock' for the purpose of delaying the strike to allow negotiations to continue, they refused."    

Even though studios have stockpiled scripts in preparation for a strike, production of many sitcoms is expected to shut down this week since writers will not be able to go on set and offer last-minute rewrites. The impact on movies is seen as less immediate since the major studios already have scripts for next year's projects.

Counter said the studios tried to meet the WGA on the key issues, but he said the union was unwilling to compromise on most of its major demands.

A spokesman for the WGA, which represents roughly 12,000 screenwriters, was not immediately available for comment. But the Web site of the WGA's East Coast arm said the studios walked out of the talks, and it told members to report for picketing duty on Monday morning at Rockefeller Plaza, where General Electric Co.'s NBC network is located.

Earlier in the day, WGA members in Los Angeles loaded trucks with picket signs, bottled water and tables to prepare for demonstrations. Picket lines will go up at 14 major film and TV studios including Walt Disney Co.'s movie operations and ABC network, Time Warner Inc's Warner Bros., Viacom Inc'sParamount Pictures, CBS Corp's CBS, and News Corp.'s Fox.

Union members have been told that picketing is compulsory. They must sign up for four-hour shifts, and will be given signs, chants and red T-shirts emblazoned with "United We Stand" when they arrive on site, the Los Angeles Times reported on its Web site.

The WGA announced its strike plan on Friday, hours after the contract expired. Counter called the plan "precipitous and irresponsible." WGA negotiator John Bowman said: "We have to inflict as much damage as quickly as possible in order to get this thing over."    

The last major Hollywood strike was a Writers Guild walkout in 1988 that lasted 22 weeks, delayed the start of the fall TV season and cost the industry an estimated $500 million.

Los Angeles economist Jack Kyser said a similar strike now could result in at least $1 billion in economic losses.  -Reuters