Missing ceiling tiles reveal wires and beams. The faint smell of mold lingers. Water drips onto the track bed. Dark spots stain the concrete walls. Escalators don’t move, and safety cones and other equipment greet customers when they get off the trains.

Welcome to one of Metro’s busiest stations: Farragut North.

The rail stop, at Connecticut Avenue and L Street NW, looks more like a construction zone. In fact, it is. Crews are installing additional support for a water main that runs above the underground platform, and tiles need to be replaced after a street construction accident sent a chunk of concrete through the station’s ceiling in November.

To protect the water main and a sewer line, Metro is building a concrete column on the platform near the L Street exit and is putting in “a new casing and supports.” The work is expected to cost about $3 million.

At one point, the project was expected to take about two weeks in early 2010. This past winter, Metro officials said it would last into the summer. And now they say it won’t be completed until later this year — or perhaps early next.

“It is taking longer than anticipated,” said Metro spokesman Dan Stessel. “It is labor -intensive and complicated.”

Over the years, moisture from the water main has reached the concrete and caused some “structural issues we need to address,” Stessel said.

The difficulty is finding time to pour the concrete for the support, he said.

“It is no easy task to do concrete pours when you’re in a large space, and it is even more of a challenge when you’re in a confined space,” Stessel said. “This is not the kind of project that can be done with trains and customers in the mix” because it requires a lot of manpower and equipment.

Already, Red Line trains operated on a single track between Dupont Circle and Judiciary Square on two weekends in July. There will probably be two more weekends of single-tracking this fall to do some of the work, Stessel said.

Work to repair the ceiling tiles will be done after the support column is in place, Stessel said. Metro officials said the District is expected to pay for the repair work. The cost is unknown.

Farragut North, the fourth-busiest stop in the Metrorail system, is used by commuters traveling to the city’s core business district and tourists heading to the nearby White House.

The station is dimly lit. A walled-off construction area near the L Street exit leaves a narrow stretch of the platform where passengers can walk. Bags of concrete mix, wires, pipes, and other supplies and equipment sit at the far end of the platform.

“When you get off the train, it is kind of restrictive to walk along the platform,” said Robert Anglin of Madison, Wis. “There’s equipment when you get off, and it looks like it’s been under construction for some time.”

Mary Hetrick of Coventry, Conn., found it slightly nerve-racking to walk with her 7-year-old granddaughter along the narrow stretch of platform. “I was so scared walking by there with her,” she said.

Some riders said they would like to see more signs explaining the work and how long it is going to take.

Swarms of rush-hour commuters often find themselves getting off trains and then lining up to walk up one of the nonmoving escalators from the platform to the mezzanine near the K Street exit. On Thursday morning, three of the four escalators from the platform to the mezzanine were out of service.

One escalator is undergoing a major rehab as part of Metro’s $150 million plan to repair and refurbish escalators. The work is expected to be completed in November. Another was shut off so that people could use it to walk either up or down. The other is out of service because of a water leak overhead; it is expected to be working soon.

“I can’t remember when there were working escalators,” Susan Haag, a lawyer, said as she waited in line to climb the stairs with her purse and briefcase on her shoulders.

“It’s frustrating,” Nicholas Robbins said as he climbed the stairs one morning. “It puts a frown on your day.”