Montgomery County officials say all but three of the county's 317 computer systems have been fixed in preparation for the next millennium, effectively concluding a mammoth project that has consumed years of staff time and millions of dollars.

County Executive Douglas M. Duncan's administration set Sept. 30 as the deadline to have all computer systems repaired or replaced to function in 2000. And for the most part, county officials have met that goal: Computers that run stop lights, track grades at public schools and send out tax bills--among other services--have been deemed safe to face the year 2000.

The remaining "low-priority" systems are in the final testing stage and should be Y2K ready by the end of the month, giving county officials a cushion before the computer clocks roll over to Jan. 1. The systems monitor the school bus fleet, help some personal computers communicate with the county mainframe system, and expedite some database searches.

County officials also have delayed certifying four other computer systems run by the Montgomery Housing Opportunities Commission. Those computers have been repaired, county officials say, but the agency has not submitted a required contingency plan in case disaster strikes on New Year's Day.

"The key thing is that three months out we believe we are in a state of readiness," said Bruce F. Romer, Montgomery's chief administrative officer, who supervised the Y2K project.

Romer will deliver that assessment today to the Montgomery County Council, a group that has raised questions about the cost of the project from its inception three years ago. In an interview yesterday, Romer said the final bill for the county's Y2K project will total $47.2 million.

That final cost--about $56 per Montgomery resident--is about $3 million higher than originally requested. But Romer said a $5 million reserve fund included in the budget to fix last-minute Y2K problems will not have to be used. "We do not anticipate requesting any additional funding to do the work we have left," he said.

In a county enchanted by high-technology--public buses are outfitted with satellite navigation equipment and residents may soon be able to track their tax bills online--the Y2K problem promised to be a bear from the start.

The programming flaw derives from the fact that many older computers process dates by the last two digits, assuming the first two would remain 1 and 9. When that changes at midnight Dec. 31, unprepared computers could read the date as 1900 and crash.

Montgomery's program, held up as a model on "60 Minutes" and other national news programs, has remained largely on track. By contrast, the District is entering its final three months amid deep confusion over how its $120 million Y2K program is progressing.

Montgomery County Council President Isiah Leggett (D-At Large), who has questioned the cost of the county's program, said some of the spending has gone to purchase new systems ahead of schedule that would have had to be replaced anyway.

"We have been killing two birds with one stone," Leggett said.

By contrast, Fairfax County plans to spend $3.4 million preparing for Y2K--a fraction of Montgomery's budget. But those figures do not include work done by the school system, as it does in Montgomery, and Fairfax officials acknowledge that they chose to buy far less new equipment than Montgomery.

"We did more repair than replace," said Jim Brown, the county's Department of Information Technology Y2K coordinator.

As part of Montgomery's program, county agencies are required to submit a list of back-up procedures in case the best laid Y2K plans fall apart. For example, the county will print January payroll checks in December. Also, county officials will prepare W2 income tax forms and make a bond payment a month earlier than scheduled rather than risk the uncertainties of January 2000.

"We think this is a good completion to a long process," Romer said.