American Telephone & Telegraph Co. has mistakenly billed the families of about 25,000 U.S. military personnel in Saudi Arabia for phone calls to the United States the troops made during a call-home-for-free campaign last month.

However, AT&T officials blamed the whole thing on a massive computer foulup and promised yesterday that no one in Operation Desert Shield will have to pay the bills, some of which ran to several thousand dollars.

The bills angered some servicemen and women who learned that their family members had been charged for calls they made home. "This has affected virtually every soldier in our unit," one Military Police officer said.

"Nobody has to pay" the bills, AT&T spokesman Richard Wallerstein said yesterday. The international telecommunications giant is crediting the accounts of families that paid already and telling complaining callers to ignore the notices, he said.

"It's as if it never happened," Wallerstein said. "There's no way we're going to charge people for our mistake."

Wallerstein said the improper bills resulted from a botched computer program instruction to local phone companies that send out AT&T's long distance call bills. The computers were supposed to suppress the charges for anybody who took advantage of the offer, but in many cases the instructions never took hold.

AT&T first made the call-home-for-free offer in mid-October and cut it short a week later after being swamped with more than 130,000 phone calls. It revived the campaign for Thanksgiving, between Nov. 20 and Nov. 27, generating another 140,000 phone calls.

The offer was popular because direct-dial calls from Saudi Arabia to the United States cost about $16 for 10 minutes. AT&T had asked troops to limit the calls to three minutes, but the time limit was "self-policing" and was widely ignored. Sgt. Thomas Blue, stationed with a Military Police unit in Saudi Arabia, said, "Virtually every soldier that I know in our unit made phone calls home" under the policy. He said he had made "four or five" calls to "my parents, my sister and my grandparents" and talked up to an hour to each of them.

While his family had not received the bill yet, other members of his unit were reporting bills "from $600 to $2,000, really exorbitant amounts. . . We were shocked and amazed. I feel very misled."

Wallerstein said AT&T was not reviving the offer for the troops in Saudi Arabia during the Christmas season, but had offered free call-home service to members of the Navy and Marine Corps stationed on ships in the Middle East.