Agriculture Secretary John R. Block has proposed cutting the food stamp program by another $1 billion in fiscal 1984, sources said yesterday.

In a Sept. 17 letter to the Office of Management and Budget, Block also proposed folding a number of child-feeding programs, including school breakfasts, the summer feeding program and the Child Care Food Program, into a single block grant.

In addition, Block suggested eliminating food aid to day care facilities in private homes, as well as canceling his department's funding of school nutrition programs operated by the Defense Department and the Interior Department's Bureau of Indian Affairs.

These cuts could reduce outlays for child nutrition programs by several hundred million dollars, unless they are made up by other agencies, according to program experts.

The new food stamp cuts would be on top of substantial reductions that Congress has approved in the program over the past three years.Congress has tentatively approved a fiscal 1983 budget for the program of $10.8 billion, or about 20 percent below the level before President Reagan took office, according to one expert.

The OMB refused to discuss any details of the Block proposal, but one source said," There has been an awful lot of discussion since Sept. 17," and Block's proposals may have been altered substantially since then.

The biggest cut proposed by Block would increase the "benefit reduction rate" from 30 percent of a recipient's net income to 33.3 percent. Under this proposal, a family's current annual benefits would drop by an amount equal to 3.3 percent of its net income, after certain deductions are made.

A family of three with an annual gross income of $6,100 would see their monthly allotment of $99 worth of stamps cut to $88; an elderly couple with $475 a month in Social Security income, now getting $264 a year in stamps, could be cut to $120 a year.

Although Block did not cite any savings figure, one expert estimated that the proposal would reduce benefits by at least $650 million.

A second proposal would simplify and combine certain deductions from income now allowed in the program, and, according to Block, provide "some benefit reductions."

A third would give states a fixed block grant for administering the program at the local level, thus saving the federal government added expenditures if state administrative costs exceeded the grant.

A fourth suggestion would eliminate any benefit under $10 a month, a proposal that the Reagan administration made last year but Congress has failed to approve. Block said this would affect only house holds at the upper end of the eligibility scale. However, experts said that under certain conditions, it could mean a person with income as low as $285 a month could lose all his benefits and it could hit elderly and disabled persons heavily.

A fifth proposal would give persons on Supplemental Security Income cash in lieu of food stamps.