Americans turning 65 this year can expect to live, on average, until they are 83, four and a half years longer than the typical 65-year-old could expect in 1940. And government actuaries predict that American life spans will just keep growing. 

This demographic trend - by 2040, the average 65-year-old will live to about 85 - has major financial implications for Social Security and major political implications for the lawmakers now trying to overhaul the system.

Policy experts across the political spectrum, who agree on little else, have told Congress in recent weeks that any effort to improve Social Security's long-term finances should somehow deal with this jump in life expectancy - by adjusting benefits, raising the retirement age, increasing taxes or creating new incentives to work longer. 

Not only are Americans living longer, these experts say, but most are also retiring earlier, and these demographic pressures will be heightened by the sheer size of the baby boom generation - 78 million strong - which will begin to retire in the next five years.

Major committees in the House and Senate, struggling to produce Social Security legislation this summer, are beginning to confront the longevity issue. Senator Charles E. Grassley, Republican of Iowa, the chairman of the Finance Committee, says the retirement age will be addressed in the solvency plan he hopes to develop with his fellow party members in the coming week, and his Republican counterparts in the House are holding hearings on the issue on Tuesday.

"We've got to deal with reality," said Senator Trent Lott, Republican of Mississippi.

But the politics are treacherous, all the more so because Republicans are dealing with it alone. Democrats have refused to engage in discussions over Social Security's finances until President Bush withdraws his proposal to create private investment accounts in the program.

The most direct way to deal with the financial strain of greater longevity is simply to raise the retirement age, which now stands at 65 years and 6 months and will gradually rise under current law to 67 for people born in 1960 and later. But of all the options to shore up Social Security's finances, that ranks as one of the most unpopular, pollsters say. In a New York Times/CBS News Poll earlier this year, nearly 8 out of 10 respondents said they would oppose raising the age when people are eligible for Social Security benefits.

Political strategists say this issue is viewed very differently by policy experts, who may see nothing wrong with working longer, and average Americans, with jobs that may be uninteresting, stressful or physically demanding, who are often eager to retire and doubtful of their employment prospects in their mid-to-late 60's. 

"In Washington, the focus is on the demographic reality that people live longer, and most of the people who are having this conversation wouldn't mind working well into their 70's and 80's," said Geoff Garin, a Democratic pollster. "But out in the country, most working people don't look forward to working forever."

Glen Bolger, a Republican pollster, agreed: "Forty might be the new 30, but they don't necessarily believe that 70 is the new 65."

Lawmakers in both parties have acknowledged that many people not only want to but also need to retire at 62 or 65. Representative Bill Thomas, Republican of California, the chairman of the Ways and Means Committee, recently reflected, "I know my father, in terms of his plumbing activities, was pretty - the phrase, I guess, would be pretty used up by the time he was 65."

Representative Earl Pomeroy, Democrat of North Dakota, a committee member, said, "I represent a lot of people doing some pretty hard labor out there on those farms."

As a result, many analysts say any proposal to deal with increased life expectancy would probably include some protections for low-income workers in physically taxing fields. There are other potential inequities associated with raising the retirement age: on average, women live longer than men; whites live longer than blacks; the rich live longer than the poor.

Another political hurdle is AARP, the lobby for older Americans, which notes that a major increase in the retirement age is already under way as a result of the last significant overhaul of Social Security, in 1983. The normal retirement age, as the Social Security Administration calls it, is to rise by about two months a year until it reaches 67 in 2027. (One proposal occasionally discussed is simply speeding up the increase to 67.)

Workers can take earlier retirement at 62, as most do, but their benefit checks are reduced as a result - 20 percent or more every month for the rest of their lives, depending on how early they retire.

David Certner, director of federal affairs for AARP, said, "Just because you raise the age, doesn't mean there will be jobs out there so you can continue working, even if you want to." Moreover, he added: "you've got a whole group of people who are just not physically or mentally able to continue. I think a lot of people recognize that if you change the age, you just push those people onto the disability rolls," which are financed by the same Social Security taxes as retirement benefits.

Still, experts say that the system as a whole needs to reflect the new demographic realities. C. Eugene Steuerle, a senior fellow at the Urban Institute and a former official in the Reagan administration, notes that Americans already retire, on average, for close to one-third of their adult lives, and argues that Social Security "has morphed into a middle-age retirement system."

The change in the last 60 years is striking: The average retirement age in 1940 was 68. As recently as 1965, about two-thirds of workers did not begin drawing Social Security benefits until they were 65 or older. Now, more than half retire at 62 or younger, and three-quarters receive their first benefit checks before they are 65.

Edward M. Gramlich, a governor of the Federal Reserve Board and an authority on Social Security, says that if the architects of Social Security "had known about the explosion in life expectancy, they would have put in some adjustment in the retirement age."

One way to address the problem - and the direction some lawmakers seem to be heading in - is an automatic adjustment in the retirement age or the benefits received at each age to reflect increases in life expectancy. That way, retirees' total lifetime benefits would remain more or less constant even as they lived longer. Automatic changes are already made for average wage increases and price inflation.

For individuals, such a change, called indexing for longevity, would be little different from a direct increase in the retirement age or a specified reduction in benefits, said Douglas Holtz-Eakin, director of the Congressional Budget Office. But for the system, Mr. Holtz-Eakin said, it would make a big difference because the changes would be automatic and would not require new laws.

It might also be politically attractive because politicians would be relieved of the responsibility of periodically voting to raise the retirement age or to cut benefits.
Adjusting the system for longevity would not contribute much to solving Social Security's solvency problem over the next 30 years or so, Mr. Holtz-Eakin said. But over 75 years and longer, he said, it would have an important effect.

Still, pollsters question whether even a gradual adjustment based on life expectancy will sell. "You can call it indexing for longevity in Washington, but in America it's raising the retirement age," said Mr. Garin, the Democratic pollster. Mr. Bolger, his Republican counterpart, said, "There's no appetite for anything related to age among the public."