Yesterday was liberation day for Gary Hill, the day when he could say farewell to his Honda CVCC and the traffic snarls along I-270 in Montgomery County. Yesterday, Hill boarded the commuter train in Gaithersburg for the first time, on his way to his job 25 miles away in Rosslyn.

With the opening of Metro's Blue line, which gave commuters from Gaithersburg access to Virginia by railroad and subway, the 39-year-old computer expert has embarked on a new way of life and after 11 years of being wed to the steering wheel of his car two hours a day

Standing on the open platform of the Gaithersburg railroad station at 6.45 a.m., he bubbled like a 10-year-old.

"This is like Christmas morning for me," he said. "This has got to be tremendous . . . Driving home was getting to be a terror." He smiled, eyes sparkling under his strawberry-blond hair. "My whole life-style is going to change dramatically . . . We're giving up one of our cars."

Hill joins about 2,000 riders who take the train back and forth from Washington each day along the Chessie system line that runs from Harpers Ferry to Union Station.

The Blue Line, with its access to major employment centers like Rosslyn and the Pentagon drew him aboard for the first time, undoubtedly as just one of many new Chessie riders who will be attracted by the subway.

The expected boost in the number of passengers will be a mixed blessing for the railroad line. Its ridership has increased by nearly 60 per cent over the past two years. Already many of the commuters who board in Gaithersburg have to stand for most of the 38-minute ride to Union Station.

The opening of the Blue Line will give other seasoned Chessie riders a chance to do what 17 per cent of their fellow-passengers already do: transfer to the subway at Union Station, instead of taking a bus or walking to their offices.

"We're hoping it will make a difference, in our commuting time," said Doris McLaughlin, who got on the train in Brunswick. Both McLaughlin and her husband, Lloyd, spend 3 1/2 to 4 hours daily getting form their home in Lovettsville,, Va., to their jobs at the Department of Agriculture and back.

"We're hoping we can cut an hour off that," she added. Her husband explained. "With the subway, we're looking to catch an earlier train out of town and a later train in."

The bus trip form Union Station to Department of Agriculture used to take as long as a half-hour. With the Blue Line in operation, the couple will be five stops and one change of trains away: about 10 minutes.

Ed Plamer and David Scott, neighbors in the Quince Orchard section of Gaithersburg and colleagues at the U.S. Forest Service, used to walk the mile and three-quarters between Union Station and their offices in the morning and evening.

"The Blue Line is a little more palatable," said Scott, who is also a relative newcomer to the Chessie commute.

But no one on the train had as dramatic a reaction to the new possibilities of Metro as Gary Hill. "The Washington area has no idea yet what Metro can do for it," he said.

"This whole thing is a holiday. I look forward to it," even though "I may lose a few minutes" in work time.

His estimate was about right: he arrived at the offices of DUALabs in Rosslyn at 8:25 a.m., almost a half-hour later than he usually does, but still a full hour before the offices officially opened.

But the time didn't matter to him, not when he thought of that Friday a few weeks ago when the drive home took him 2 1/2 hours - without accidents and without rain.

Now, he plans to take the 5.25 p.m. train back to Gainthersbyrg daily, and maybe get into a station carpool with Jim Cole, a neighbor and fellow commuter he met on the train.

Between his savings on gas, car insurance and the $25 monthly parking fee he had been paying, Hill figured that the $65 a month he will pay for his new commuting will be a net gain.

He now feels that eight years of noise and dust beneath his ninth-floor office window in Rosslyn as the subway was being constructed was worth it. "I've sat and watched this for eight years," he said. "You'd be sitting in your office and all of a sudden the office floor would move. The blasting, you know.

It looks like it was worth it."