‘O’ is the letter of the ‘Law’

If not for the absence of an all-important “o,” Julianna Margulies might never have considered doing “Canterbury’s Law,” a new Fox legal drama.

Having starred in “ER,” the 41-year-old actress knew the grind of doing 22 episodes per season. So when she started looking for a new show to do, Margulies had cable in mind, reasoning that there would be fewer episodes per season, meaning higher quality and a less demanding schedule than with a broadcast-network series.

“Then I got the script for ‘Canterbury’s Law.’ ” She liked it, and liked the fact that it was from Denis Leary and Jim Serpico, producers of “Rescue Me,” the acclaimed series about New York firefighters that airs on the FX cable network.

“I called my agent and said, ‘I’ll do it,’ ” Margulies recalled in an interview. “He said, ‘But it’s Fox.’ I said, ‘No, it’s FX.’ I looked at the cover letter again. Whoever it was who wrote it had left out the ‘o.’

“When I realized the network was Fox,” she says, “it was a tough decision.”

She decided to proceed, however, and the show premieres Monday.