Telephone companies went on alert yesterday after being told that computer "hackers" may try to disrupt telephone communications today, company officials said.

Where the disruptions may occur was not known, other than the attacks would be leveled against computer programs and routines, not physical facilities.

"We have not been able to assess the validity of the threats, but we certainly take any threats seriously, and we've taken precautions to minimize the risk of intrusion," BellSouth spokesman Bill McCloskey said.

"We are aware of the purported threat to try and disrupt at least part of the nationwide network," said Herb Linnen, a spokesman for American Telephone & Telegraph Co. "Our corporate security organization has sent word around the country to make sure everyone is on alert in the coming days."

Linnen said the purported threat was against "telecommunications facilities" and not necessarily against any single company. He said the rumor of the attempted disruption came from internal and external sources, and that it was discussed at a regular meeting Wednesday of technical executives of a number of phone companies.

"We have no idea how widespread the threat might be," said Peter Goodale, a spokesman for Nynex Corp., parent of the New England Telephone and New York Telephone companies. "We've taken the appropriate security measures to ensure the integrity of our network."

The Federal Bureau of Investigation and Defense Department officials said they were unaware of any such threat.

Industry sources who asked not to be identified said the threat appeared to be connected to the sentencing scheduled today in Atlanta of three members of a hackers' group that called itself "Legion of Doom." The three men, Franklin E. Darden Jr., Robert J. Riggs, and Adam E. Grant, pleaded guilty earlier this year to charges in connection with breakins of BellSouth Corp. computers.