Internet traffic slowed and major news Web sites were jammed Tuesday as people craving details on the World Trade Center and Pentagon attacks flooded online.

But the Net also proved its mettle as a communications facilitator in a time of crisis.

Electronic mail was a godsend for many people trying to reach loved ones but frustrated by clogged telephone voice circuits, and Web sites were established to help people find out whether friends and family survived.

The Internet search engine Google directed news seekers to radio and television. "Many online news services are not available, because of extremely high demand," a statement read on the popular site's home page.

America Online's Instant Messenger service was sporadic in New York throughout much of the day.

AOL's dial-up connections in New York were constantly busy, although the service was sometimes reachable by making long-distance calls elsewhere. AOL spokesman Jim Whitney said the service was running normally from the company's end. He did report a slight spike in instant-messaging traffic.

Keynote Systems Inc., which measures Internet performance, said that in the early hours the Web sites it tracked took longer to reach nearly 13 seconds, compared with a daily average of five. Performance improved by late afternoon.

The WIRE and other Internet services run by The Associated Press experienced more than five times the normal traffic, said company spokeswoman Kelly Tunney.

"All of our news distributions systems have been stable despite the tumultuous amount of traffic," she said.

E-mail proved crucial, meanwhile, for many people seeking to reach families and friends in the chaos and uncertainty that followed Tuesday's destruction.

While telephone calls produced busy signals, quick e-mail messages confirmed that loved ones were alive.

Gretchen Heefner of San Francisco quickly went online to check on several close friends in Manhattan. "Send word when you can," she wrote.

"I could not reach anyone on their home phone, cell phone or work phone from my home phone or cell phone, and so e-mail was the best way," she said. "Fortunately, people were in their offices and have fast connections and could get their e-mail right away."

EBay and other sites added messages of sympathy to their home pages. EBay also banned until Oct. 1 the sale of any items relating to the World Trade Center or the Pentagon.

Prodigy Communications Corp. created an "I'm OK" online message center to let people find information about loved ones. Visitors enter their name, location and a brief message stating they are "OK."

Berkeley graduate students also established a site. One student, Miriam Walker, got the idea after roommates encountered difficulties calling the East Coast.