Sean Schuback, a 15-year veteran of Verizon, arrived at work one morning last December to unsettling news: A company e-mail sent the night before announced that the telecommunications giant was freezing its pension plan.

In an instant, Schuback, 33, who joined the company as a phone operator right out of high school, saw the $469,286 pension payout he was told he could receive by working another 15 years sliced to $245,494, where it would stay no matter how many more years he put in.

"When I started, I thought, 'This is just a job for a while,' but the benefits were so good I stayed," said the Eastchester, N.Y., resident, who worked his way up to a managerial position. Now, his plan to retire early at 48 and work part time is dashed.

What happened to Schuback's pension is part of a long-running trend, as otherwise healthy companies — not only Verizon Communications Inc., but also International Business Machines Corp. and, most recently, DuPont Co. — freeze, terminate or alter the terms of their employees' retirement packages. Most of these companies increased other retirement offerings, which don't include fixed payouts.

Today, about 22 million workers, 19 percent of active private-sector employees, have traditional pension plans, compared with 39 percent three decades ago, according to federal government statistics.

Despite Schuback's financial setback, any retirement expert would say that Schuback should count his blessings as one of a dwindling number of U.S. workers who have a benefit that many say is quickly becoming a dinosaur.

"There's no doubt, if you have some guaranteed retirement from your employer, you are definitely in the lucky minority," said Jack VanDerhei, a professor in the business school at Temple University and a research fellow at the nonprofit Employee Benefit Research Institute.

He and other financial experts say workers fortunate enough to still have traditional pensions should not rely on them too much for retirement, as the long-term prospects of such plans are increasingly in doubt. While a new law signed last month by President Bush aims to shore up the private pension system by forcing companies to fund their plans more fully, some retirement consultants say the added expense may accelerate the trend of companies limiting their plans for existing employees or dropping them for new hires.

As workers make their retirement calculations, they should keep in mind the two sometimes opposing principles that govern the U.S. pension system and that the new law, the Pension Protection Act, reaffirmed: An accrued pension can't be wiped out, but companies can walk away from promised future benefits at any time.

That means workers who still have pensions will have to do more homework to determine how much money their plans are likely to provide, experts say. And they should be prepared for the worst-case scenario.

"It's always wise to cast a jaundiced eye on a pension and ask what happens if it doesn't deliver as promised," said James McGrath, a financial planner in Rockville, Md.