LOS ANGELES — Late night comedy shows were the first casualties of the first strike by Hollywood writers against TV networks and movie studios in nearly two decades.

“The Late Show With David Letterman” and “The Tonight Show with Jay Leno,” went into reruns after writers on both coasts headed for the picket line.

The walkout became inevitable late Sunday after last-minute negotiations between the Writers Guild of America and the Alliance of Motion Picture and Television Producers failed to produce a deal on such key issues as how much writers are paid when their shows are available on the Internet.

No new negotiations were scheduled, although the writers guild negotiating committee did plan a meeting of its members.

A chief negotiator for the producers union, Nick Counter, said he expected a long standoff.

“We’re hunkered down for a long one,” he said. “From our standpoint, we made every good faith effort to negotiate a deal, and they went on strike. At some point, conversations will take place. But not now.”

In Los Angeles, writers planned to picket 14 studio locations in four-hour shifts between 9 a.m. and 5 p.m. each day until a new deal is reached.

Writers said the next move was up to the studios.

“My hope is that it won’t be too long,” a chief negotiator for the writers, John Bowman, said. “We have more reason to get together than not.”

Bowman said behind-the-scenes communication was occurring between the two sides with the hope of arranging more meetings.