On New Year's Eve, top Pentagon officials withheld news of a major Y2K computer glitch that had cut access to a critical satellite intelligence system, telling reporters only after the big millennial celebrations in Washington and New York had finished.

Throughout Friday evening, Pentagon officials told members of the news media that the change to the year 2000 was proceeding without a hitch throughout the defense establishment. But yesterday the same officials revealed that a major computer failure occurred shortly after 7 p.m. EST--which is midnight Greenwich Mean Time, the time standard for many satellite systems.

A ground-based computer system that processes information from a major satellite intelligence network failed after 2000 began at Greenwich Mean Time, and the military lost the ability to collect data from the satellites, Deputy Defense Secretary John J. Hamre said yesterday at a Pentagon news conference.

"We did have one significant problem, one that I had wished we hadn't had, but we did," Hamre said. "One of our intelligence systems, a satellite-based intelligence system, experienced some Y2K failures last night shortly after the rollover of Greenwich Mean Time. And for a period of several hours, we were not able to process information from that system."

However, at a 9:30 p.m. briefing Friday, more than two hours after the system went down, the Pentagon denied that it was having any problems with computers misreading a two-digit date of 00 as 1900 rather than 2000.

"We've been monitoring the state of the world very closely, and particularly our systems, as we rolled past Greenwich Mean Time at about 1900 this evening, 7 p.m. And I'm happy to report and continue to be encouraged to report that all the Department of Defense systems remain in green status," Rear Adm. Robert Willard, head of the Y2K task force for the Joint Chiefs of Staff, announced at the Friday briefing.

"Our systems thus far are free of year 2000 glitches," he added.

As Willard was speaking to reporters, military programmers were completing a temporary repair of the processing unit that allowed it to start working again, though at reduced capacity, officials said.

Asked yesterday why the breakdown was not reported to the public on New Year's Eve, Hamre said he arrived at the Pentagon as Willard was giving the briefing and did not learn about the problem until a half-hour later.

From 11 p.m. to midnight EST, Hamre hosted a small reception in his offices for members of the news media and Pentagon officials who were keeping the millennial watch--including Willard. There was extensive informal conversation about Y2K matters, but even though the intelligence system had been fixed for more than an hour at that point, no mention was made that it had had any problems.

Even after officials and reporters watched the fireworks at the Washington Monument from the Pentagon parade ground and returned to the Pentagon's public affairs offices, officials continued to insist that all systems were operating flawlessly.

Around 2 a.m., well after the crystal ball had descended at Times Square and the nationwide live television audience had shrunk substantially, word of the computer failure was leaked to reporters.

"We did not want to release incomplete information," said a senior Pentagon public affairs officer.