Low birth weight and infant mortality occur far more frequently in low-income rural counties. And although these problems have been decreasing nationwide, they have been increasing in recent years in the rural areas, according to a report yesterday by Public Voice, a consumer research and advocacy organization.

Rep. Leon E. Panetta (D-Calif.), one of several House members at a news conference, blamed the increases partly on "severe cuts in 1981 and 1982" in federal food programs for the poor. He said the time has come for Congress to "strengthen the domestic food-assistance programs."

The news conference was called to promote a food-aid bill now pending in the House and a forthcoming farm bill that would also increase food aid.

"These new, important findings do not surprise me," said Panetta, chairman of the House Agriculture nutrition subcommittee. "In my investigations and hearings throughout the country in the past three years . . . I have found hunger to be a widespread and persistent problem. Where there is hunger, health problems cannot be far behind."

Rep. Beryl Anthony Jr. (D-Ark.) said a "misdirected policy" of cuts in food and health programs in 1981 and 1982 had harmed the health of the rural poor. He called poverty and health problems in rural areas "a national disgrace."

Rep. J. Roy Rowland (D-Ga.), a physician, said very low-birth-weight babies -- under 3 1/2 pounds -- are "200 times more likely to die in the first month" than babies of normal weight.

The Public Voice study, supported by the Ford Foundation, covered rural counties where at least a third of the population in 1979 was below the government's official poverty line. Using government health statistics it found:

*The proportion of low-birth-weight children in 85 rural counties, which had fallen to 8.21 per 1,000 live births in 1980, rose steadily after that and reached 8.73 per 1,000 live births by 1983, the last year for which figures were available. The rate in the rest of the nation, meanwhile, fell from 6.81 per 1,000 in 1980 to 6.73 in 1982.

*Infant mortality -- the proportion of children dying in the first year of life -- in the rural counties, which had dropped to 15.82 per 1,000 live births in 1981, rose to 16.55 in 1982 and then, according to Public Voice executive director Ellen Haas, leveled off to 16.29 in 1983. At the same time, the rate in the rest of the nation fell from 11.9 in 1981 to 10.89 in 1983.

Rep. Mickey Leland (D-Tex.), chairman of the House Select Committee on Hunger, said the study demonstrates that the rural poor suffer a "widening gap in their well-being compared with the rest of the country."