Jokes in short supply as talk show hosts return

Problems booking celebrities would prove especially painful for Leno, O'Brien and Kimmel. They are barred by strike rules from preparing scripted material for their shows that union writers would normally produce, so presumably they will need to fill more time with guests than Letterman.

The strike adds a new dynamic to a Leno-Letterman rivalry that dates to Leno being chosen over Letterman, then NBC's late, late-night host, to take over "The Tonight Show" after Johnny Carson retired in 1992.

Letterman jumped to CBS and outrated Leno for the first two years. But Leno's populist tone propelled him to the top of the pack, even though critics generally prefer Letterman.

(Editing by Bill Trott)