The government's food stamp program for the poor would be cut by nearly $1 billion in fiscal 1984 and child nutrition programs by about $380 million under a proposal drafted by top administration officials about two weeks ago for consideration by President Reagan, sources said yesterday.

Under the plan, food stamp spending authority in fiscal 1984, which begins Oct. 1, would be $10.2 billion.

That is several hundred million dollars less than estimated 1983 spending and $970 million below the $11.1 billion that the program would cost in fiscal 1984 if there are no changes in eligibility rules or benefits.

Child nutrition spending authority would be $3.3 billion in fiscal 1984 under the proposal, which is $380 million below the level anticipated with no changes in the law.

Administration officials declined comment on the contents of the proposal, although one did say that the draft plan is "several weeks old" and has been revised. Another said that food program cuts had been under review by the White House and that the draft plan does not necessarily reflect final decisions by Reagan, who reportedly turned down some changes.

A Capitol Hill source said that the numbers "sound like what we were hearing this morning" on administration plans for food program cuts.

Food stamps already have been cut by several billion dollars in each of the past two years at Reagan's request. The proposed reductions, if finally recommended by the president and approved by Congress, would be in addition to these earlier cuts.

Under the food stamp proposal, as outlined in the documents describing the plan, certain special deductions allowed people who have extra-high housing costs, child-care costs and certain types of medical costs would be eliminated and a standard deduction allowed instead.

The result would be about $290 million less in food stamps for people who previously had taken deductions of this type.

In the benefit calculation, stamps decline as income rises.

In addition, states that made errors in food stamp eligibility would be penalized by cuts in the administrative funds they receive for the program.

A proposed "zero error rate" for fiscal 1984 would reduce payments to states by $420 million, according to the document.

Imposition of mandatory "workfare" requirements for stamp recipients was estimated as saving another $90 million, and changes in the way food stamp benefits of welfare recipients are calculated another $95 million.

In child nutrition, the largest cut would come from melding the current school breakfast, summer food and child-care programs for low-income children into a single general nutrition assistance grant to the states, which, at $559 million, would be at least $200 million less than the combined total of the three programs to be eliminated.

There also would be savings from eliminating an extra 2-cent-a-meal payment that schools receive if they are in low-income areas, and from raising the current 40-cent-per-meal charge to near-poor students who do not qualify for free meals but do qualify for reduced-price meals.

The plan also called for $1.06 billion in budget authority for the women-infant-children's (WIC) food program, a special program to maintain the health of low-income babies and pregnant women, the same amount as 1983, without any increase to compensate for inflation.