The hotel workers’ union, shaken by a booming real-estate market that has made it profitable for developers to convert hotels into condominiums, is seeking to draw the line with the 800-room Plaza hotel.

The New York Hotel Trades Council, as the union is called, attracted a large crowd of sympathizers to a rally yesterday in front of the iconic hotel, protesting its conversion into 200 luxury condo units by its new owners, Elad Properties.

The Plaza is not the only hotel that is facing closure. A number of Manhattan hotels have already been converted into residential condominiums, with the quantity of rooms lost last year outpacing the number gained. According to a consulting firm, PKF, Manhattan lost 970 hotel rooms as of August 2004, while gaining only 577. As the residential sales market has thrived in recent months with interest rates remaining low, owners of more hotels have been considering selling to developers.

“There is not a hotel out there that is not at least looking at the numbers and considering the options,” one real-estate consultant, Esther Muller, said. “The landscape is changing, and it may be that soon hotels are found in Long Island City instead of Manhattan.”

In the past year the union has lost 1,076 jobs to hotel attrition, a spokesman, John Turchiano, said. The Plaza, with 900 union jobs and 200 nonunion managerial positions, would nearly double the figure.

Hotels that have been turned into apartments in the past year include the 208-room Intercontinental Central Park South, which is being converted into 67 luxury co-op units; the Empire on West 63rd Street, which is being transformed into 125 condo units, and the Windsor, also with 125 units. Other hotels are converting just some of their rooms, such as the St. Regis, which is transforming more than 50 of its 315 rooms into residential condominiums and launching a $15 million renovation of the remaining rooms.

“The hotel industry has the second highest tax revenue, behind Wall Street, and the city cannot afford to lose it because of a blip in the real estate industry,” the president of the hotel union, Peter Ward, told The New York Sun. “The city has invested nearly $1 billion in the expansion of the Javits Center at the behest of the hotel industry, and it is that self-same industry that is divesting themselves of rooms for a short-term profit.”

Mr. Ward said the Fairmont Hotel, which sold the Plaza to Elad Properties, lobbied for the Javits expansion and should not have sold the property to Elad in what he termed “a middle-of-the-night deal.”

“We will build the Javits Center, and in three years when it opens there will be 5,000 less rooms, and nowhere for anyone to stay,” Mr. Ward said.

“What we’re trying to do is to find ways to make sure that we don’t lose too many hotel rooms to condominiums, because we need hotel rooms for people to come here,” Mayor Bloomberg, said yesterday. “Tourism is a very big industry and an awful lot of jobs for people, so we’re trying to work with Peter Ward who represents the hotel workers and with the developers.”

The mayor added: “It’s a question of can we find ways to encourage them to have more hotel rooms, because the more hotel rooms you have, the more the jobs will be protected. But it’s a sign of success that people want to live here and are willing to buy rooms in hotels and turn them into condominiums.”

Mr. Ward and representatives from Elad met with the mayor Wednesday evening to find a compromise.

“We had a cordial exchange and agreed to meet again,” Mr. Ward told the Sun. “The fact we were in the mayor’s presence, and he was urging us to win for the city, win for the workers, and win for Elad, was something.”

Elad Properties plans to close the hotel April 30 for 16 to 18 months to reopen the building with the condominiums, a 150-room hotel facing 58th Street, and 150,000 square feet of retail space.

According to a letter written by Mr. Ward to union members and obtained by the Sun, Elad accepted a union offer this week to pay employees double severance if they agree not to be recalled to work to the new, smaller hotel Elad plans to open at the Plaza. Elad had originally rejected the offer, which Mr. Ward estimates will cost $10 million. According to the union’s contract, severance is four days’ pay for each year of service.

Mr. Ward said in his letter that the union was withdrawing the offer Elad eventually accepted.

“I believe we have a reasonable possibility of preserving more jobs, more of the building, and retaining the Plaza’s character as a hotel,” he wrote. “I also believe that in consideration of recent events there is certainly a better deal than what is now on the table. I conclude that Elad Properties does not really intend to have a hotel on the property and is only saying they do for public relations purposes.”

Elad’s president and chief executive, Miki Naftali, did not return a telephone call from the Sun.

In its efforts to head off the conversion of the hotel, the union, in conjunction with preservationists, is asking the city’s Landmarks Preservation Commission to give landmark designation to the public spaces in the interior of the Plaza. The outside of the hotel has already been given landmark status and cannot be changed, but the interior is not protected. The commission has yet to place the item on its calendar, the first step in considering a request for landmark status.

While the union is pressing its fight, the developers are forging ahead with the conversion plans. The two leading auction houses, Sotheby’s and Christie’s, remain in negotiations with Elad Properties, vying to auction off the contents of the hotel this spring after its doors close. While experts say that most objects in the hotel are of little value, the auction houses are determined to land the job because of its “cachet as celebrity real estate,” a source familiar with the auction plans said. The auction would take place sometime in the spring.

“Save for the doorknobs and the silver service that has the Plaza logo, I cannot imagine that anything is worth very much,” the author of “Inside the Plaza,” Ward Morehouse, said. Even pieces of furniture inside the Frank Lloyd Wright suite and the Vanderbilt Suite are copies, experts said. There is a painting of Eloise hanging in the public area of the Plaza, which is on loan from the painter, Hilary Knight, and in the Oak Bar are murals from Everett Shinn, a member of the Ashcan School, although it is unclear whether these murals would be auctioned.

“These objects may be worth something to people who have honeymooned here or want to take a piece of the Plaza home,” Curt Gathje, author of “At the Plaza,” said.