The nation's electric power industry said yesterday that it has fixed year 2000 computer problems in 99 percent of critical generating systems and that the plants already fixed could supply enough power to meet expected electricity demand in North America when the new year begins.

"If New Year's Day 2000 was tomorrow, we believe the lights would remain on," said Michehl R. Gent, president of the North American Electric Reliability Council (NERC), an industry group that is coordinating Y2K electric power remedies.

Potomac Electric Power Co. and Baltimore Gas and Electric Co. both said they were ready for the year 2000.

Virginia Power,, however, did not report itself fully prepared for the changeover. A spokesman said three of the company's 84 power plants are not ready but will be by this fall, when the plants are taken out of operation for routine maintenance. The company will not need power from the three plants to cover demand in January, the spokesman said.

Nationwide, 63 of 251 major power-generating utilities had at least one system that had not been tested or fixed as of June 30, NERC reported. Some utilities have delayed Y2K repairs because of the heavy electrical demand during this summer's heat wave.

Most systems at the 63 utilities have been checked and are ready for the year changeover, Gent said. The remaining repairs are designated as not critical because the demand for electricity next New Year's Day will be much less than the system's capacity, Gent said.

In addition, 8 percent of public power-distribution systems and 13 percent of electric power cooperatives have not completed year 2000 remedies. But virtually all investor-owned utilities, which supply three-quarters of the nation's electricity, report they have fixed the problems.

John A. Koskinen, head of the Clinton administration's year 2000 task force, said utilities with remaining problems must not let repairs slip late into the year, when time will be running short. The fixes are required because many older computer systems were not designed to distinguish between the years 1900 and 2000 and could break down when the new year begins.

Energy Secretary Bill Richardson said his department will make a small number of spot audits to test utility company preparations.

About one-quarter of power companies have performed internal audits of their year 2000 readiness, and the same percentage have hired outside contractors to check their preparations, said NERC year 2000 coordinator Gerry Cauley.

NERC also reported that 68 of the nation's 103 nuclear power reactors have reported completing year 2000 actions. Of the remaining 35, two-thirds require repairs to reactor systems.

Decommissioned nuclear plants will not be brought on line, and scheduled plant retirements will not be delayed to supply more power for the year 2000 changeover, according to the Nuclear Regulatory Commission.

The power industry's Achilles' heel is the telephone network that ties generators to distribution systems and controls the transmission of electric power from one region of the country to another, officials said. A year 2000 failure of phone communications could cripple power systems, and utilities plan to have backup satellite or radio links in place and tested.

The next major test of power systems and backup communications networks will occur Sept. 8 and 9.