Amid sweat and sentiment, the downtown YMCA at 1742 G St. NW closed last week.

The fitness buffs who had made the downtown YMCA a fixture in their lives marked the passing of the old building the way the Irish mark the passing of an old friend. In public, they were animated. In private, they were melancholy.

"Well this is it." said one of the regular lunchtime basketball players as he stood near a courtside bench. "The final day."

"Yeah," came a reply from the middle of the bench. "We ought to at least cut down the nets."

Completed in 1906, the rambling building was sold several years ago. A new seven-story YMCA is rising at 17th and Rhode Island Ave. NW. The opening of the new building was to have coincided with the closing of the old one. But construction slowdowns caused by last winter's severe weather have delayed the debut. It is now scheduled to open in stages - the first stage set for mid-January, the last for the beginning of April.

In the closing hours of the old YMCA last Wednesday afternoon, the mood was festive. Runners bounced around the tiny indoor track, being careful not to whack their elbows on the metal posts holding the track to the gymnasium ceiling. In the pool, veteran members of the Nautilus Club took their final laps.

The afternoon volleyball game, sometimes sedate and short-handed in the past, was boisterous and well-attended. One player even got there early to stroll around the old building and snap a few photographs.

In the locker room, there were signs of transition. Several locker doors hung open, their works rusted, their dull green paint peeling. A broken squash racket was stuffed into a trash can.A blue duffle bag, minus handles, had been abandoned.

During the days before the closing, conversations among the regulars centered on how much they would miss the old building and what they were going to do without it.

"I've been coming to this stinking, rotten hole for 15 years," Gideon Hadary said as he stood in the dimly it gym. "And I am going to miss it. It has become a habit."

Hadary, an executive with the Virgin Island Refinery Corp. in downtown Washington, had just finished his regular noontime excercises. He wore a bright yellow T-shirt soaked with sweat. As he spoke, chips of paint occasionally dropped from the ceiling, landings on th dusty gym floor.

"I started coming here because I worked downtown. Now I even drive in from Chevy Chase," he said. "It's a custom. I arrange my day around it. I come down here, exercise and then go to lunch."

Hadary, 58, said that he plans to join the new YMCA. But in the interim, "I'm going to be a very unhappy old man," he said.

"I've got to go now," he grinned, mentioning a luncheon date at one of Washington's finer French restaurants. "I'm going to eat a very flattening meal."

Jim Vitagliano said that he has been coming to the YMCA for 20 years to run and work out with weights. The old building was near the National Aeronautics and Space Administration where he works. And he explained, after 20 years, he felt a certain attachment to the old YMCA.

"The equipment is old. I think Lincoln used the weight room," Vitagliano mused. "But you develop a feeling for the equipment."

To demonstrate his point, Vitagliano quickly worked the combination to the padlock on his locker.

"I don't know the combination to this lock; I don't know it by the numbers," he said. "I just do it by the feel."

Vitagliano, a well-muscled man, looks much younger than most other men who are 42 years old. As he took off his shirt and tie, his biceps bulged.

The time lapse between the closing of the old YMCA and the opening of the new one is going to cause him some problems, he said. Until then, he plans to work out at home.

"But you get a much better workout in a gymnasium," he said. "You have a limited amount of time and so you go in the gym, do your exerise and get out. Just as you study better in a library, you work out better in a gym."

Sam Raff, a physicist with the National Science Foundation, said he would miss playing racketball at the old YMCA.

"The courts are lousy, but it is fun. When you get to be my age - 57 - you play a lot of strategy against these young tigers," Raff said.

With a smile, he acknowledged that his strategy included knowing the quirks of the old YMCA courts.

"I even know where the wet spots will be when it has rained," he said.

Some veterans of the old YMCA have vowed that they will not join the new one. According to them, the costs are outrageous. But YMCA officials said the fees are justified and will keep the new YMCA out of the red.

At the new facility, YMCA offiicals said, a general membership, or fitness center fee, costs $325 per year, plus a $200 inititation fee. A deluxe membership, or athletic center fee, includes the use of a sauna and ultraviolet lights and costs $495 each year - plus a $250 initiation fee. The yearly rates at the old YMCA ranged between $100 and $285. The initiation fees at the old facility were $25 for those holding the least expensive memberships and $50 for those with the more expensive ones.

However, Thomas B. Hargrave, general executive of the downtown YMCA, said this week that while membership fees at the new YMCA may seem high, a limited-use membership plan makes the Y "within reach of everyone."

In this plan, members pay lower rates, but use the YMCA during off-peak times. The initation fee is $25 and annual dues range from $128 to $195 a year. Members who join under this limited-use category may use the YMCA all day Saturday and Sunday, but only after 7 p.m. on weekdays.

The YMCA has mounted a two-part campaign to raise $2 million, needed to help pay for increased construction costs of the new $5.3-million building. The orginial estimates listed construction costs at $3.7 million and site acquisition at $1.5 million, both covered by funds from the sale of the old building.

Hargrave said that so far $670,000 has raised toward first-phase gola of $1 million. The first phase, which is largely a drive for donations, will end this spring, when the second part of the campaign will begin. Hargrave said second phases will focus on raising funds through initation fees.

But as the regulars cleaned out their lockers the old YMCA last week, most seemed to agree with the veteran racketball player, Raff. He wasn't sure how he felt about the new YMCA, he said, but he knew how he felt about the closing of the old one."It is kinda sad," he said.