Subway trains were ready to roll at 5:30 this morning, after a last-minute financial offer by D.C. Mayor Anthony A. Williams persuaded Metro to get moving early instead of 8 a.m. as planned.

"One of the things the mayor has a whole lot of is just some plain common sense," said his spokeswoman, Linda Grant. "We've got a lot of things going on here, with the millennium and Y2K, in addition to running the city, but he saw that people responsible for being at work needed the means to get there."

The schedule change will mean the longest day of service in Metro's history; trains will run from 5:30 a.m. today until 3 a.m. tomorrow.

Metro originally planned to begin service at 5:30 a.m. But when the federal government refused to help pay an estimated $1.8 million to carry a record number of New Year's Eve passengers this weekend, the agency opted to start service at 8 a.m. to save $50,000. It also dropped the tradition of free fares after midnight, saying revelers must pay their own way. Metro has not reversed itself on fares.

"We were in a standoff with the federal government," said Jim Graham, a member of the D.C. Council who also serves on the Metro board. "Frankly, I'm glad we blinked."

Metro is in good financial shape and expects a budget surplus this year.

But its directors insisted the federal government should kick in money for New Year's Eve service, because the White House plans a "national" celebration on the Mall that will attract out-of-towners.

The transit system expects riders to make as many as 750,000 trips, more than double the number for a normal New Year's Eve.

In defending their decision to open later, Metro directors noted that today is both a federal and District holiday.

But today is a work day for many in law, financial services and--especially, with millennium celebrations--the hospitality industry.

Concerns about Y2K problems also mean many government offices will have skeleton work crews.

An 8 a.m. start would have given Washington the lowest level of holiday service among the country's major transit systems. New York, Chicago, Philadelphia, Boston and San Francisco are running either 24-hour service or service that began today at 4 a.m. or 5 a.m.

The 8 a.m. plan earned the scorn of commuters, a dozen of whom telephoned and sent e-mail to Metro to complain they were being stranded.

As late as yesterday morning, the chairman of Metro's board of directors, Katherine K. Hanley, was appearing on television news programs, telling viewers the 8 a.m. start was unavoidable.

But hours later, Hanley and the others changed the schedule and accepted the mayor's deal. The District agreed to pay $25,000 for 5:30 a.m. service, if the other jurisdictions that subsidize Metro--Virginia and Maryland--paid the remaining $25,000.

At an emergency meeting of the Metro board yesterday, members unanimously approved the arrangement. Managers scrambled to line up an extra 160 workers needed to run the trains and stations.

News of the 5:30 a.m. opening was cheered by commuters and employers.

"I'm delighted," said Lynn Rollins, director of marketing at the Hay-Adams Hotel, where management was planning to hire private vans to pick up hotel workers who were to start shifts at 7 a.m. today and had no other way to get to work.

"This is one less thing to worry about. It shows the city cares. . . . We want our staff to focus on our guests, not transportation."

But others wondered if the schedule change came too late.

"I'm lucky--I know because you called me," Ken Breznay, a bank executive who planned to take Metro to arrive at his job by 8 a.m., told a reporter.

"A lot of people are going to miss it. I'll bet the trains will be running quite empty because people won't know about it."