WASHINGTON (AP) _ Negotiators for UPS and the Teamsters union continued to meet early Friday past a midnight deadline in an attempt to avert a strike against the giant delivery service.

Matt Witt, a Teamsters spokesman, said shortly after midnight that strike plans were put on hold, but added that could change at any moment.

``There's no limit on how long we'll talk or how long we'll hold off a strike,'' he said.

UPS spokeswoman Gina Ellrich said the company had seen no job actions at any of its facilities around the country as of early Friday.

Ron Smith, business agent for Teamsters Local 728 in Atlanta, said workers at the UPS distribution center there were told to go home and report to work Friday as long as the negotiations were continuing.

Benny Stephenson, Local 728 organizer, said, ``I guess that's a good sign.''

Top officials of the Teamsters and the company met with a federal mediator in Washington past midnight, but there was no word on whether any movement was being made toward a settlement.

UPS spokesman Ken Sternad said in Atlanta: ``UPS and the Teamsters union have agreed to continue to meet in an attempt to reach agreement on a new contract. ... We intend to do everything possible to reach an agreement without disrupting our service.''

However, UPS took out a full-page ads Friday in major newspapers telling its customers to expect a disruption in service.

In what it called ``an open letter to UPS customers,'' the company said it has been unable to reach an agreement with the union.

``Under these circumstances, we can no longer promise uninterrupted delivery service,'' the ad said. ``We will, however, make every effort to continue to serve customers.''

The UPS ad appeared hours after John Calhoun Wells, director of the Federal Mediation and Conciliation Service, met with the lead negotiators from each side to try to kick-start the stalled talks.

``They have returned to the table,'' said Steve Trossman, a Teamsters spokesman. ``We are committed to doing what we can to reach a contract that meets the needs of Teamsters members. But if we don't reach agreement, we're prepared to strike.''

After what union officials said were productive meetings in recent days, the talks stalled when company negotiators abruptly presented what UPS said was its final offer late Wednesday night.

``We look at this as another bargaining tactic,'' said Teamsters spokesman Rand Wilson, who welcomed the mediator's participation. ``We will not agree to this contract.''

``We have made a last, best and final offer to the union,'' Sternad said earlier. ``We put it on the table late last night when it became apparent that there was not going to be an agreement.''

Nevertheless, Sternad said the company remained open to discussing its proposal with the union.

White House spokesman Mike McCurry said top Clinton aide Bruce Lindsey had met with negotiators. ``It's been mostly an informational session ... so that the White House will be abreast of collective bargaining discussions they've been having,'' McCurry said.

UPS, based in Atlanta, has 302,000 U.S. employees, about two-thirds of them Teamsters. Only the U.S. Postal Service employs more workers under a contract.

A UPS message to customers Thursday said, ``We are advising our customers that after the contract expires, delivery delays may be possible.'' The company had sought a contract extension, but the Teamsters declined.

UPS' 2,000 pilots, represented by the International Pilots Association, have pledged to join the Teamsters in a walkout.

Competitors such as Federal Express Corp. and the U.S. Postal Service were making contingency plans, but analysts say it would be difficult to make up UPS' volume of 12 million parcels and documents a day.

The Teamsters waged an aggressive campaign to build support for a strike if needed, but on Thursday the company distributed leaflets at work sites, alleging that union leaders were blocking a good deal.

The Teamsters' Wilson said the company had already ``moved closer to meeting our members concerns'' in informal talks between lead negotiators,

``We expect them to come back to the table and get real,'' he said.

Along with increases in pay and pensions, the Teamsters have pressed UPS to limit subcontracting, strengthen safety and health provisions and create more full-time jobs. About two-thirds of the Teamsters-represented employees are part-time workers.

A key sticking point was the company's insistence on ending its participation in the union's multi-employer pension and health funds to establish a separate UPS benefits pool.

The company said that in addition to a modest wage increase, its offer included a $3,060 bonus for full-time employees and $1,530 for part-timers. If profit goals are met, the bonuses would be repeated in two years.

Full-time UPS drivers earn $19.95 an hour on average.

UPS also said it had created 1,000 new full-time jobs and given part-timers a leg up in applying for full-time posts when they become open. The Teamsters want more full-time jobs.