WASHINGTON — Millions of older people face smaller Social Security checks next year, the first time in a generation that payments would not rise.

The trustees who oversee Social Security are projecting there won't be a cost of living adjustment — COLA — for the next two years. That hasn't happened since automatic increases were adopted in 1975.

By law, Social Security benefits cannot go down. Nevertheless, monthly payments would drop for millions of people in the Medicare prescription drug program because the premiums, which often are deducted from Social Security payments, are going up slightly.

"I will promise you, they count on that COLA," said Barbara Kennelly, a former Democratic congresswoman from Connecticut who now heads the National Committee to Preserve Social Security and Medicare. "To some people, it might not be a big deal. But to seniors, especially with their health care costs, it is a big deal."

Cost of living adjustments are pegged to inflation, which has been negative this year, largely because energy prices are below 2008 levels.

Advocates say older people still face higher prices because they spend a disproportionate amount of their income on health care, where costs rise faster than inflation. Many also have suffered from declining home values and shrinking stock portfolios just as they are relying on those assets for income.

About 50 million retired and disabled Americans receive Social Security benefits. The average monthly benefit for retirees is $1,153 this year. All beneficiaries received a 5.8 percent increase in January, the largest since 1982.

More than 32 million people are in the Medicare prescription drug program. Average monthly premiums are set to go from $28 this year to $30 next year, though they vary by plan. About 6 million people in the program have premiums deducted from their monthly Social Security payments.

Kennelly's group wants Congress to increase Social Security benefits next year, even though the formula doesn't call for it. She would like to see either a 1 percent increase or a one-time payment of $150.

The cost of a one-time payment, about $8 billion, could be covered by increasing the amount of income subjected to Social Security taxes, Kennelly said. Workers pay Social Security taxes only on the first $106,800 of income, a limit that rises each year with the average national wage. But the limit increases only if monthly benefits increase.

Critics argue that Social Security recipients shouldn't get an increase when inflation is negative. They note that recipients got a big increase in January — after energy prices had started to fall. They also note that Social Security recipients received one-time $250 payments in the spring as part of the economic stimulus package.

Consumer prices are down from 2008 levels, giving Social Security recipients more purchasing power, said Andrew G. Biggs, a resident scholar at the American Enterprise Institute think tank.

Sen. Bernie Sanders, an independent from Vermont who is working on a proposal for one-time payments for Social Security recipients, said, "I think a lot of seniors do not know what's coming down the pike, and I believe that when they hear that, they're going to be upset."