Private pension coverage is declining among U.S. workers - particularly younger employees - suggesting future retirees may depend more on Social Security and other kinds of retirement income, a government report says.

The share of full-time private workers participating in employer-financed pension plans fell to 46 percent last year, from 48 percent in 1983 and 50 percent in 1979, according to a report in Social Security's monthly bulletin.Because coverage rates probably were underestimated by 1 to 2 percentage points in 1979 and 1983, the decrease may be more pronounced, the report said.

The decline represents a reversal from the growth of earlier decades, when pension coverage rose from about one-fourth of private workers in the early 1950s to one-half by the late 1970s.

The statistics "suggest decreasing rates of private pension receipt among future generations of retired workers and a corresponding increased reliance on other sources of retirement income, including Social Security benefits," the report said.

The Employee Benefits Research Institute, a non-profit research group, attributed the decline in part to employment shifts toward industries with lower pension coverage and to a drop in the number of union workers, whose coverage rates are higher.

Merton Bernstein, a law professor at Washington University in St. Louis, said employment has been shrinking in areas such as manufacturing that traditionally have had high rates of pension coverage. Areas where employment is expanding, such as service and retail jobs, traditionally have low pension coverage, he said.

He said less pension coverage would cause a greater drain on many government services.

Future retirees without private pensions "may have to delay retirement or they may have a very inadequate income. The less adequate income is, the more demand there is for other government services, such as medical care and supplementary income," he said.

The Social Security report, written by John R. Woods of the agency's Office of Research and Statistics, found the declines in pension coverage "have been concentrated among younger workers, and primarily among younger men."

Coverage among those ages 16-24 dropped by 10 percentage points, from 31 percent in 1972 to 21 percent last year, and coverage rates fell 6 percentage points for those 25-29 and 4 percentage points for those 30-34. Coverage was virtually unchanged for those 35-54 and rose for those 55 and older.

The report said coverage rates for women, which traditionally have lagged behind those for men, have been steadily gaining ground, with the gap narrowing from 16 percentage points in 1972 to 6 percentage points by 1988.

Last year, 49 percent of full-time male workers were covered, compared with 43 percent of women.