The D.C. government will lose about $4.4 million next year in funding for health and social service programs--primarily in maternal and child health care and alcohol and drug treatment--under the Reagan administration's "New Federalism," according to figures released yesterday by Mayor Marion Barry.

The loss in these federal funds, all of which will be channeled for the first time through six block grants, will have "a deteriorating effect" on service for low-income persons who use city-supported treatment facilities, city budget director Gladys W. Mack said in an interview.

The figures released yesterday represent an estimate of the amount to be lost and a broad outline of how Barry proposes to spend the remaining monies when the fiscal year begins Oct. 1. Mack said officials have not yet determined precisely how the cuts will be implemented.

"These cuts force us to provide services at a reduced rate," Barry said in a letter to the City Council, "so that in some areas there will be screening of clients where this had not been necessary before; and in other cases there will be an increase in the waiting time for assistance of all clients, and some services will be eliminated."

The plan outlined by Barry represents the city's first major planned effort to cope with the newly created block grant system, in which some 33 separate grant programs formerly administered by the federal government will now be lumped into six categories run by the local government. According to D.C. government estimates, the city will receive $25.4 million for six federal block grants in fiscal 1983, a reduction of about 15 percent from the $29.8 million received this year. The six blocks are maternal and child services; preventive health; alcohol, drug abuse and mental health; social services; community services; and low-income energy assistance.

Mack said the cuts are actually far less than earlier projections, in which the city thought it would lose $11 million. Nonetheless, she said, the city's "tenuous" financial situation will make it impossible to absorb the block grant cuts without cuts in services. A $1.1 million contingency fund could be used to offset part of the federal cut, she said.

The losses outlined by Barry include:

* $1.7 million out of the $3.8 million received in the current fiscal year for alcohol and drug abuse programs.

* $1.6 million out of the current $6.2 million for maternal and child health programs.

* $400,000 out of this year's $2.9 million to provide heating assistance for low-income persons.

* $240,000 out of the current $448,000 for rodent control.

* $120,000 out of this fiscal year's $295,000 for a crippled children's program at D.C. General Hospital.

Barry pledged to maintain basic city programs for infant and maternal health, drug treatment, day care and care for the elderly. But to do so, he said, other unspecified services would have to be cut back.

Barry's recommended spending plan, which will be reviewed at a City Council public hearing Friday at 10 a.m. at the District Building, closely follows the recommendations of a 30-member Block Grant Advisory Committee he appointed May 12.

The Reagan administration has touted the block grant strategy as a way to give greater decision-making power and flexibility to state governments.

Some city officials, however, have termed the New Federalism program "shift and shaft" because the shift of responsibility has also included budget cuts and therefore has created intense competition for money among public and private social service agencies.

"If we had $5 million to run seven programs, now we will have $5 million to run 11 programs," said Barbara Sabol, chief of policy and planning for the city Department of Human Services (DHS). "Something has to give."

"Where we could have seen you in 20 minutes in a health clinic, now you may wait an hour and a half" because staffing levels may be reduced by attrition, she said. "Or your appointment next week will become two weeks from Wednesday."

Sabol said such reductions in service could be serious in maternal and child health, where the goal of city clinics has been to deliver intensive care early in pregnancy to help reduce infant mortality.

"It's going to be incredible," said Dr. Arthur H. Hoyte, the city commissioner of public health, in reference to the anticipated competition for block grant money.

In the current fiscal year, Hoyte said, the city received $6.2 million that was used to run three city-operated maternal and child health clinics, and to fund similar health programs at hospitals and clinics around the city.

For fiscal 1983, he said, the city will have only $4.7 million to run the same programs, but will also be receiving requests for funding from other health facilities, including hospitals, that formerly received money directly for the federal government.