Even as networks delay or drop potentially sensitive episodes and clip violent scenes in terrorism's immediate wake, network executives expressed uncertainty Tuesday about how deep or lasting the effects of Sept. 11 will be.

"Everyone wants to see this as a demarcation line in popular culture, and it may very well prove to be," NBC Entertainment President Jeff Zucker said. "But I think it's too early to know exactly what that is."

The attacks bumped the official start of the new season a week, to Monday. While networks gingerly returned to regular fare after grueling, nonstop news coverage, viewers seemed eager for the change.

"You can see it in the prime-time ratings," Zucker said. "Clearly, people are looking for some diversion and clearly that is role that entertainment can play."

A repeat episode of Friends with the wedding of Monica and Chandler on NBC last Thursday drew 17.6 million viewers -- unusually high for a rerun.

Late-night shows returned somberly last week, but already have returned to comedy.

In general, networks took no chance of giving offense: Even a lightweight comedy like Ellen, the new CBS series starring Ellen DeGeneres, was subject to revision.

DeGeneres' character spoke in Monday's premiere episode of losing her job in the dot-com collapse. Her mother's reply -- "I hope you didn't get caught in the building" -- was removed from the show.

The change was made "in light of the recent tragic events," the network said, referring to the terrorist destruction of New York's World Trade Center towers and damage at the Pentagon.

In an upcoming Friends episode, changes are being made in a scene in which newlyweds Monica and Chandler (Courteney Cox and Matthew Perry) run into airport problems on their honeymoon.

More problematically, a number of new series are set in the world of the CIA or other government agencies, with stories that edge perilously close to aspects of the tragedy.

CBS pulled the pilot episode for The Agency, which opened with a Middle Eastern scene of a booby-trapped hostage, a U.S. flag stuffed in his mouth as a gag, dying in an explosion.

Airing in its place Thursday will be an episode about a plot to assassinate Cuban leader Fidel Castro.

In the new Fox series, 24, a drama starring Kiefer Sutherland as the head of a U.S. counterterrorist unit, the pilot included a now-edited scene in which a bomb explodes on a plane. The show debuts Nov. 6.

NBC has scrapped a script with a terrorist story line for the new action series UC: Undercover, which starts Sept. 30 and focuses on a Justice Department crime-fighting unit.

Lloyd Braun, ABC entertainment chief, said Tuesday he wondered whether viewers would have much patience for reality shows with petty conflicts when the real news is so dramatic.

"I'm not sure the country is going to be as accepting of these shows as they've been in the past," he said. "You have to wonder whether people are going to look at that and say, 'please, I don't care.'"

There have been a number of other changes, including the removal of potentially unsettling shots of the World Trade Center from programs including NBC's Law & Order: Special Victims Unit.

In contrast, NBC's White House drama The West Wing is tackling the issue of terrorism head-on in an episode written by series creator Aaron Sorkin. The administration of President Bartlet (Martin Sheen) will be shown coping with fallout from a terrorist attack in the Oct. 3 episode. The planned season premiere episode was moved to Oct. 10.

"We didn't feel comfortable going back to our fictional White House without taking a moment," executive producer John Wells told Daily Variety. "Hopefully, we can say something that's useful and not at any way appear like we're trying to exploit the tragic events that occurred."