With the start of the New Year just five days away, Clinton administration officials said yesterday the Year 2000 computer problem should cause few, if any, disruptions.

"We would like people to be prepared for a long mid-winter weekend, but we think that that's all that's necessary. And for most Americans, they probably won't experience any Y2K glitches at all," said John A. Koskinen, the president's Y2K troubleshooter.

Power plants, air traffic control and federal prisons are Y2K ready, and 95 percent of 911 emergency response systems have been fixed, Koskinen and other administration officials said.

The government's top aviation safety official, Jane F. Garvey, reaffirmed that she still plans to travel cross-country on a jetliner as the New Year begins. But she acknowledged that only "a very small number" of commercial flights will be in the air on the night of Dec. 31.

Garvey, head of the Federal Aviation Administration, will be aboard the only American Airlines flight taking off that night in the continental United States. She will leave Reagan National Airport before 7 p.m. Friday--midnight Greenwich Mean Time for the air traffic control system--and land in San Francisco shortly after midnight West Coast time.

"That day, generally, not a lot of people are traveling. But we'll know more as we get closer to the day, the actual number, and we'll be watching all of them," Garvey said.

Many airlines have cut back their Friday flights by as much as 20 percent because of a lack of advance bookings. British-based Virgin Atlantic plans to shut down as a way of giving all of its employees "family time" for the holiday, Garvey said.

"Air traffic will be safe," Garvey said. "Certainly if it wasn't safe, we wouldn't allow the planes to fly, so we'd keep them on the ground." She said the destinations abroad where most Americans usually fly "are in very, very good shape."

The administration officials offered their upbeat assessments on ABC's "This Week," one of a series of appearances this month aimed at reassuring the public that Y2K presents no more of a threat than the inconveniences of a winter storm.

The White House has urged citizens to have on hand a three-day supply of food and water, batteries for flashlights and copies of important financial records. While the White House has recommended that motorists keep tanks above half full, they also have asked drivers not to overreact and top off their fuel tanks unnecessarily late this week.

The Commerce Department estimates that the nation has spent about $100 billion to avoid Y2K problems through computer repairs, system replacements and extensive tests. But not all countries have mobilized to squash the so-called millennium bug.

Russia, in particular, lags on its Y2K fixes. Yesterday, Deputy Defense Secretary John J. Hamre said the administration has spent $10 million to help Moscow, partly to avoid confusion if early warning systems give off false alarms about nuclear missile launches.

Hamre said Russian military officers will join their U.S. counterparts this week in Colorado Springs to monitor early warning systems and ensure timely communication between the two nuclear powers. "We're very confident that the missiles are just not going to be launched," Hamre said.

Asked if he was worried about hackers taking advantage of Y2K to launch cyber-attacks on defense computer networks, Hamre said the Pentagon has been working with software companies to update ways of detecting and preventing the spread of "viruses that hackers are trying to implant in systems. . . . We'll be ready for that."

Despite their overall confidence about U.S. readiness, administration officials remain worried that some small hospitals and doctors are at risk of Y2K glitches that could jeopardize their finances.

Virtually all hospitals and numerous physicians use computers to file claims for insurance payments from the federal government's Medicare and Medicaid programs, but little is known about the Y2K status of their billing systems because of incomplete responses to federal surveys.

"Most of them don't have much cash-flow cushion, and if they have difficulty with their systems and can't get reimbursed, they'll have major financial problems," said Koskinen, chairman of the President's Council on Year 2000 Conversion.

The year 2000 problem, popularly known as Y2K, stems from the use of two-digit date systems in many computers that might cause them to misinterpret "00" as 1900, not 2000, and malfunction or shut down.

Koskinen has said he expects Y2K problems to pop up as late as March as large corporations and the government process data and prepare their first end-of-the-quarter financial statements. Yesterday, he pointed out that 2000 is a leap year and "it turns out enough people didn't understand that," raising the possibility that computers may spew out bad data starting Feb. 29.

Administration officials said some programmers did not do the proper calculations when writing their software instructions and, as a result, did not give 2000 that extra day. Other programmers simply did not know 2000 is a leap year, they said.

The error should not pose any widespread problems, but Koskinen said "we will monitor whatever happens on the 29th just the way we are monitoring what happens over the weekend of January 1st."

CAPTION: Y2K coordinator John A. Koskinen, left, says Americans need only "be prepared for a long mid-winter weekend" come Jan. 1. Federal Aviation Administration chief Jane F. Garvey says she will be in the air New Year's Eve to show her confidence in air traffic control. And Deputy Defense Secretary John J. Hamre says the United States has spent $10 million to help the Russians avoid problems, particularly with missile systems.