he New York Police Department expects to pay up to $1.7 billion in overtime this fiscal year, a sum more than five times the record overtime it paid last year to officers who worked extra hours or extra shifts.

The enormous expansion in overtime, as the city responds to security concerns caused by the World Trade Center attack, will have serious implications for the city's budget, even though large federal reimbursements are expected. But analysts say it could have an even larger impact on the department itself: the accelerated retirements of veteran officers who stand to qualify for larger pensions because of exceptionally large salaries this year.

New York City, which already has an acknowledged problem with police retirements, is about to pay many of its veteran officers an average of $50,000 in overtime for the current fiscal year, which ends June 30, 2002. That sum will nearly double their salaries and create a huge incentive to retire while pensions reflect the unusually large earnings.

"Anyone contemplating retirement before, this overtime will definitely make them decide on retiring," said Joseph Maccone, who managed the department's pension unit last year and now works for the police officers' union.

Through September, 1,677 of the city's 40,000 police officers retired, up 75 percent from the same period last year. Mr. Maccone said there were early indications that 500 more officers filed for retirement in October, up from 161 in October 2000.

"Everybody that was on the fence, now can't afford to stay," said one Manhattan detective who plans to retire in several months. He said he would make $90,000 this year, far more than the $75,000 he anticipated. "I have to get out. I'll never see this kind of money ever again."

Officers who serve 20 years in the job are entitled to pensions worth half of what they earned in their last 12 months with the department. Officials predict that between now and next September, the average patrol officer with 20 years of experience, who typically earns $64,000 a year with holiday pay and limited overtime, may make $110,000 or more.

For pension purposes, an officer's salary in his final year can rise only by 20 percent from the prior year, so only some of the additional earnings would be factored into the pension.

At the same time, some officers have told colleagues that, as tempting as the larger pension looks, they are worried about shrinking job opportunities in the private sector as the economy slows. And even if they want to go, only about 3,500 officers are eligible to retire with a full pension for 20 or more years in the job, officials said.

Still, the department is not taking the problem lightly. "It is a known fact that retirements were going up because of big classes that were hired 20 years ago," said Deputy Commissioner Thomas Antenen, a police spokesman. "How much of this will be affected by the overtime earned after the World Trade Center disaster remains to be seen."

So far this fiscal year, which is just four months old, the Police Department has spent $227 million for overtime, or $16 million more than budgeted for the entire fiscal year. More than half, $140 million, was spent on overtime associated with recovery operations and security patrols needed after the terrorist attack.

At this rate, city budget analysts predict police overtime may well reach $1.7 billion, a sum equal to the budget for the Philadelphia school system and five times what the Police Department spent last year, when overtime peaked at $317 million. Officials said the projection was based on the assumption that the level of security now in place would continue throughout the year.

Fire Department overtime has also increased this fiscal year. The department, which has an overtime budget of $88 million this year, has already spent about $58 million, with more than half of that attributed to the attack and its aftermath.

Officials said they were anticipating some rise in retirements but were still evaluating the potential impact of the additional earnings.

"Even though some people might be contemplating retirement," said Frank Gribbon, a spokesman for the Fire Department, "there are others who are making a commitment to stay to help the department get through this period when seniority and experience is so important."

The Police Department has already taken steps to curtail overtime spending where it can. For example, Operation Condor, a program that gave commanders overtime money to assign officers to work a sixth day in a week as they saw fit, has been suspended since Sept. 11. And much of the department, which had been working 12-hour tours in the weeks after the attack, has returned to normal eight-hour shifts.

But given the new level of security in place throughout the city, with police officers routinely patrolling bridges and tunnels and deployed in larger numbers to sporting events, even the most questioning analysts of police spending agree it will be difficult to exert much control on overtime this year. "What is happening now just can't be compared to anything that has happened in the past," said City Councilman Sheldon S. Leffler, the chairman of the Public Safety Committee. "A lot of it is involuntary because it is a response to a disaster of a magnitude that is beyond anything the department has ever faced."

Because the overtime bill and others will likely grow so large, the federal government has already begun discussions on how much of the cost it will reimburse, according to city officials. The Federal Emergency Management Agency is expected to reimburse the city for police overtime accumulated in the weeks immediately after the attack. Congress is expected to appropriate additional funds to help with the later costs.

But Preston Niblack, deputy director of the Independent Budget Office, a city agency that provides nonpartisan analysis, said it was not clear that the federal government would pick up anywhere near the full cost.

"It seems the costs that are related to new security needs are going to be on the city's own tab," he said. "The next mayor is going to face some choices about how to pay for these new needs, and cutting back on police overtime may not be as feasible a saving now as it was before Sept. 11."