Social Security benefits will rise 2.4 percent in January, the largest cost-of-living increase in three years, the Clinton administration announced yesterday.

For the average retiree, the monthly benefit amount will go from $785 to $804, the Social Security Administration said. For the average elderly couple, the benefit will increase $32, to $1,348 each month.

In addition to retirement checks, Social Security benefits are paid to about 6.6 million disabled workers and families whose primary wage earners have died. Those benefits, known as Supplemental Security Income (SSI), also will rise by 2.4 percent, effective Dec. 30. The maximum federal SSI monthly payment to an individual will rise from $500 to $512, and for a couple from $751 to $769.

The annual cost-of-living adjustment (COLA) is one of the most anticipated announcements made by the government, because it affects about 44 million Americans and because many senior citizens depend on the extra money to help them cope with the rising costs of drugs and other products.

Similar COLAs extend to federal retirees and their survivors. More than 1.6 million government retirees and families covered by the Civil Service Retirement System will see a 2.4 percent increase in their monthly checks in January. More than 100,000 retirees in the Federal Employees Retirement System will get a 2 percent COLA, officials said.

Social Security and SSI benefits are adjusted automatically each year based on the rise in the consumer price index from the third quarter of one year through the corresponding period of the next. The 2000 increase will be nearly double the 1999 COLA, which was 1.3 percent.

Working Americans also will contribute more to Social Security next year. The maximum amount of earnings subject to the Social Security payroll tax will increase to $76,200 from $72,600, the government said. That means the maximum Social Security tax paid by workers next year will be $4,724.40, an amount that employers are required by law to match.

The maximum amount that a beneficiary under 65 may earn without losing any Social Security benefits will increase from $9,600 this year to $10,080 in 2000. The maximum amount that a beneficiary age 65 to 69 may earn without losing any Social Security benefits will increase from $15,500 to $17,000.

In a separate announcement, the Department of Health and Human Services said the monthly Medicare premium deducted from most Social Security checks for insurance coverage of physician services and hospital outpatient care will stay at $45.50. Last year, it rose by $1.70.