Metro is painting the interior of its busy Farragut North station a light gray, dramatically brightening the 16-year-old downtown station but also changing the original architectural concept, which features unpainted concrete walls and ceilings.

Many riders praise the $15,000 paint job but others criticize it, saying Metro is violating the design integrity of the station and adding to maintenance costs at a time when money is tight and fares are increasing.

Unlike many subway systems, which use a different design for each station, Metro developed an identity by using the same now-familiar look for each of its 70 stations. All have coffered ceilings, most in the style of Roman barrel vaults. The ceilings and walls are made of poured concrete that is unfinished but smooth.

Metro officials say they had no choice but to coat the ceilings and entrances of Farragut North with a whitish sealant, which they say will last about 10 years. The color of the sealant becomes darker over time, so the white color riders see now will become somewhat more gray, they said.

The current effect of the painting, combined with increased lighting, seems startlingly bright to some accustomed to the old look, clashing with the gray granite on the platform edges, the red-brown terrazzo paving and bronze fixtures.

Fady P. Bassily, Metro's rail manager, said that despite a thorough cleaning of the station walls and ceilings, large, ugly blemishes remained because of poor quality concrete that was used and stains that resulted from constant water leaks. The choice was to leave the walls as they were, or try the sealant, which costs about $30 a gallon. Metro's own painters applied 500 gallons of the sealant, which looks like whitewash.

"Our options there were very limited," he said.

John J. Corley, an architect with Harry Weese Associates, Metro's architect, said no one at Metro consulted with him about the sealant, which he said is not unusual because the firm long ago finished its work on that station.

"I don't think you'd go into the cathedral at Notre Dame and paint the stonework," Corley said. "That's the question here. Is it appropriate to paint concrete? The issue is still out for further evaluation."

During early Metro construction in 1971, The Washington Post's architecture critic, Wolf Von Eckardt, praised the Metro station design, writing that, "Nothing will touch these arched walls. The structures inside -- the escalators, mezzanine platforms and even the train platforms themselves -- are free-floating within the vault, so people can't touch (and vandalize) the walls either . . . . This simple, clear, strong and vibrant basic form, poured in concrete, is structurally as efficient . . . as it is esthetically pleasing."

Farragut North, a Red Line station under Connecticut Avenue NW between K and L streets, is the first station where the sealant will be applied on much of the interior. Spot applications of the sealant will take place at other sites, such as the entrances to Metro Center. Bassily said officials are considering painting the Federal Center SW station, which also has poor quality concrete.

Farragut North, Farragut West and Metro Center are Metro's busiest stations, with about 25,000 round trips daily. Metro carries about 250,000 rail riders a day. With such exposure, the paint job is getting noticed.

"I like the brightness," said June Thaxton, of Baltimore. "I used to notice the cracks in the wall."

"I think it looks a lot cleaner," added Ralph Loveless, of Silver Spring.

But Dennis Mankin, of the District, said the sealant contradicts Metro's original design. And as the station ages, he said, the sealant will have to be applied again.

"The poured concrete interior of the stations has to me always seemed an extremely wise choice of materials, not only because of the appearance but also because it is virtually maintenance-free," Mankin said. "If they'd make this decision without asking anyone's opinion, what else will they do?"

Bassily said after Farragut North was cleaned, revealing the blemishes, a decision had to be made quickly without going through the usual channels. Besides, he said, "We've got a lot of compliments about it."

Metro board members had complained for years about the dark, dirty conditions at Farragut North.

The paint job is part of a $96.2 million, seven-year rehabilitation of Metro stations, centering first on the oldest stations downtown.