The doormen who usually accept packages, take in dry-cleaning, and carry heavy grocery bags could soon be taking off their white gloves and joining a picket line.

The union for about 28,000 doormen, elevator operators, porters, and other residential building employees is in down-to-the-wire contract negotiations and has already authorized its board to call an April 21 strike if a fair deal is not reached.

“Everything goes up, the inflation rate goes up, rent goes up, but our salaries diminish,” a doorman at a co-op building on the Upper East Side, Boris Buliga, said yesterday.

A strike of those who watch over some of the most elegant and expensive homes in the country would be the first since 1991, when the employees walked off the job for 12 days. Doormen also went on strike in 1979 and 1976.

A strike would affect 3,500 buildings across the city, including 2,500 in Manhattan, where in many cases management has just started to blanket tenants with contingency plans that call for resident volunteers to take out the trash and fill in for rotating shifts at the front door.

Both the union and management sides said they were in contract talks yesterday and would continue through the deadline.

One Gramercy Park building sent out letters to all residents notifying them that no move-ins or outs will be permitted in the event of a strike; that garbage chutes will be closed so residents will have to haul their own garbage to the curb; that a security guard will be hired, and residents will be given special identification passes to get in.

The sticking points in negotiations between the Service Employees International Union Local 32BJ, which represents the building employees, and the Realty Advisory Board are wages, pensions, and health care.

The board, which represents building management, is asking for a salary freeze for one year and that employees start kicking in 15% of health care costs or about $1,400 a year for each employee. They say that rising health care costs are putting pressure on building managers.

“We’re going to try as hard as we can to find common ground, but if we don’t the buildings will be ready,” the president of the board, James Berg, said.

A spokesman for 32BJ, Matt Nerzig, said doormen net between $500 and $600 a week and need a salary increase to meet standard cost of living hikes.

The health care contribution issue is not a new one in labor negotiations. It was one of the primary roadblocks that prompted transit workers to stage an illegal strike in December.

Mr. Berg pointed out the $31,700 doorman salary does not count about $14,000 in annual benefits for employees. It also does not include Christmas-time tips, which can be a lucrative and scarcely taxed source of income for doormen.

The building employees are not government workers, so a strike would be legal. It could, however, become a safety issue for elderly residents and prompt widespread disruption for other unionized services.

A professor of law who specializes in employment issues at New York Law School, Arthur Leonard, said a strike would likely mean no package deliveries and no home renovations because other union workers will be unwilling to cross the picket lines.

In the 1991 strike UPS workers did not cross the line. A spokesman for the International Brotherhood of Teamsters, which represents UPS workers, Bret Caldwell, said yesterday, “if there’s a picket line we won’t cross it.”

A concierge at a co-op building on 62nd and Park Avenue, Thomas Flynn, who is a member of the union, said the whole thing would be a hassle and that he hopes it doesn’t happen.

“Nobody wants to be out of work. You never make that money back,” he said. Mr. Flynn, 57, has a wife and three children and takes home about $560 a week after taxes.

He supplements his paycheck by playing in a band. He said a strike would be hard on everyone and that he would rather it didn’t happen, but that because he wants to “live and enjoy his life” he would never think of breaking ranks with his union.

Mayor Bloomberg’s office said he does not get involved in private-sector negotiations unless both sides request it. So far that has not happened.

A 23-year-old pharmaceutical representative, Lisa Arbeit, who lives in a doorman building in Murray Hill and was pulling a suitcase along Park Avenue in the 70s yesterday, said a strike would be inconvenient and unsafe.

“I don’t think it’s a good way to go about solving the problem,” she said. “Look at the MTA, they went on strike and they still don’t have a contract.”

A soprano opera singer, Rebecca Baird, said she considers the doormen “like family” and that she wants them to be treated fairly. She predicted an 11th-hour agreement.