One U.S. household in six received in-kind federal aid last year under the government's four main non-cash, means-tested programs: Medicaid, food stamps, housing subsidies and school lunches, the Census Bureau said yesterday.

The federal government has shifted increasingly from cash to in-kind welfare programs in recent years. Medicaid and food stamps are now the two largest federal welfare programs, with housing subsidies not far behind.

The bureau said 14,615,000 of the nation's 83,918,000 households were aided by at least one of the four programs last year. Market value of total benefits under the programs was estimated at $51 billion, more than twice the amount paid in cash welfare.

The number of households receiving benefits dropped by about 50,000 compared with 1981, although unemployment was higher last year. This was largely because of a decline in households receiving Medicaid, from 8.5 million to 8.1 million.

One reason for the decline may be the tightened Medicaid eligibility rules passed by Congress in 1981 at President Reagan's behest. Participation in the other three programs rose slightly last year.

Of the 14.6 million households aided by the four programs, 7.27 million, or 49.7 percent, were below the official federal poverty line: $9,862 for a family of four. Another 1.83 million, or 12.5 percent, were in the category of "near poor," meaning households with incomes up to 125 percent of the poverty line.

Excluding the value of in-kind benefits, the median income of households enrolled in the four programs was $8,030; the median for all U.S. households last year was $20,170.

Although many recipients were over the poverty line, about 4.9 million households, or 40 percent of those below the line, received no in-kind benefits. One reason is that some people with very low incomes have some savings and are thus ineligible. In addition, childless couples and single persons are ineligible for Medicaid unless they are old or disabled. Some states have also set Medicaid eligibility cutoffs well below the poverty line.

Households headed by blacks, Hispanics and women had far higher participation rates than did other groups. Of white households, only 6.3 percent received food stamps, 16.2 percent received free or reduced-price school lunches, 8 percent lived in subsidized housing and 7.5 percent were Medicaid recipients.

Among blacks, the participation rate was 26.3 percent for food stamps, 50.3 percent for free or reduced-price lunches, 24.1 percent for subsidized housing and 26.1 percent for Medicaid.

Among Hispanics, the figures were 18.8 percent for food stamps, 44.5 percent for free or reduced-price lunches, 10.8 percent for subsidized housing and 20.3 percent for Medicaid.

In households headed by women, 30.8 percent received food stamps, 47.7 percent received free or reduced-price lunches, 23.1 percent lived in subsidized housing and 31.9 percent were Medicaid recipients.