Roosevelt Islanders who rely on the aerial tramway connecting the island to Manhattan will soon have to find an alternative route.

The tramway is expected to be closed between June 10 and June 18, which will give residents a taste of the transportation woes they will face next year, when it is scheduled to be taken out of service for at least six months. Next year’s timing is inconvenient: The tram’s closure will come at a time when several hundred new residents are expected to move into two new buildings now under construction.

Some 2,000 new units will be completed in the next few years, part of a construction boom that, when completed, will have nearly doubled the island’s population. But transportation links between Roosevelt Island and Manhattan have not kept pace with the development. With the tram’s scheduled outage, the already overcrowded subway service on the F line, and ferries only a far-off possibility, advocates and elected officials are warning that the island’s transportation woes will soon reach crisis proportions if nothing is done.

“Roosevelt Island is literally bursting at the seams,” the assemblyman who represents Roosevelt Island, Micah Kellner, said. “The MTA really needs to address this, especially since the other major mode of transportation is going to be down for seven to 12 months.”

Roosevelt Island, which had a population of roughly 10,000 people in 2000, may house between 18,000 and 19,000 people by 2010, according to some estimates.

A narrow strip of land in the East River between Manhattan and Queens, Roosevelt Island is owned by the city but leased to New York State. It was long the site of hospitals and long-term care facilities, and then a number of high-rise apartment buildings were built there in the 1980s and 1990s.

In 1997, Hudson Properties and the Related Cos. were awarded the development rights to build nine new residential high-rises there. Four buildings have been built so far, with employees at local hospitals occupying much of the space. New York University also purchased a block of units in one of the buildings, Riverwalk Landing.

The fifth building, Riverwalk Court, will be ready for occupancy by the end of the year, while the sixth building, which is not yet named, will be ready in the first quarter of 2009. One-bedrooms in Riverwalk Court start at $575,000, two-bedrooms at $785,000, and three-bedrooms at $1.225 million, she said.

Plans for the last three projects are being finalized, a vice president at Related, Kimberly Sherman Stamler, said. “What’s unique about Roosevelt Island is that, no matter what apartment you’re in, you’re looking into open space,” she said. “You feel like you’re on an oasis.”

Next year’s $25 million overhaul is an effort to make the 30-year-old tram more reliable and easier to repair, the president of the Roosevelt Island Operating Corp., Stephen Shane, said. Tram safety has come under scrutiny in the last two years, following a malfunction that left commuters stranded over the East River for nearly 12 hours. “We don’t want that to happen again,” Mr. Shane said. “There will be inconvenience in the short run, but the long-term benefits will be significant.”

While the tram is down, the RIOC-operated “red buses” will take residents between the island and the Long Island City transportation hub Queens Plaza, Mr. Shane said.

Residents say the red buses aren’t dependable, even when they’re confined to Roosevelt Island. “They’re absolutely terrible,” a financial analyst who recently moved to the Octagon apartment building on the north of the island, Zack Graney, 21, said. Mr. Graney relies on the red buses for transportation to the subway and the tram.

During rush hour, the average commuter has to wait for to two or three subway trains to pass before finding space to board, Mr. Kellner said, adding that the island had only 6,000 people when the subway station was built.

“The F is always dirty and smelly and crowded,” a resident who moved to the island in January, Serife Gokdemir, said. “That’s the only thing I hate about this island.”

Moreover, like many subway lines in Manhattan, there are frequent service interruptions to the F line on weekends, with trains often not running one way or the other. Because Roosevelt Island has only one subway line, such interruptions severely hamper residents’ ability to get on and off the island, the founder of the Web log Roosevelt Island 360, Eric Schwartzman, said. As of mid-May, Mr. Schwartzman reported on his blog that Roosevelt Island had disrupted service for 13 of 20 weekends in 2008.

A spokeswoman for the MTA, Deirdre Parker, said the recent service interruptions were due to security projects in the 53rd Street tunnel and a switch maintenance job.

Acknowledging the need for more transportation options, the developer of the Octagon, Becker + Becker, has secured necessary permits for ferry service leaving from the north end of the island, but the city has said it won’t begin constructing a dock until at least 2010.

Ms. Stamler said potential buyers understand the long-term benefit of a new-and-improved tram. “We don’t think it’s going to impact us as much as people perceive that it will,” she said. “The F train is a very popular method of getting to work in the morning.”

The tram repair plan “has not been a hindrance to visitors or sales,” she added.

Mr. Schwartzman said residents are hoping for a ferry or expanded subway service in the future. But for the time being, he said, “the concern is, how is everything going to work?”