Federal food stamp assistance for about 22 million low-income Americans would be cut about a fourth under a plan prepared for President Reagan's budget director.

Reductions of about $3.8 billion over the next two years are recommended in the proposal, an example of the ways the administration is now moving to make promised cuts in federal spending.

According to a White House source, the food stamp reduction proposal was drafted by Robert Carlson, former welfare official in Reagan's California cabinet, working under the domestic policy council staff headed by Martin Anderson. The source said this plan has not been adopted by the president and that other approaches are being considered.

The incoming Office of Management and Budget director, David A. Stockman, and other administration officials have indicated the food stamp program would be one of the first places where budget savings will be sought.

Food stamp supporters in Congress already are gearing up for battle over the probable blitz on the program which is to be reauthorized this year as part of a general farm bill.

The new chairman of the Senate Agriculture Committee, Jesse Helms (R-N.C.), long a critic of growing costs of the program, has talked about major reductions in food stamp spending, ranging as high as 40 percent.

But Rep. Frederick W. Richmond (D-N.Y.), chairman of the House Agriculture subcommittee that oversees food stamps, warned recently that Reagan, Stockman and Helms are playing with fire.

He said any efforts to "emasculate" the program would seriously jeopardize urban-surburban legislators' backing of other farm commodity support programs Reagan and Helms are likely to advocate.

"This Stockman is not very realistic," Richmond said. "He is talking through his hat, overreacting because he is totally inexperienced in the politics of farm legislation.

"Without a food stamp program as part of the package, there is no way a general farm bill can pass. I have conveyed that idea to Sen. Helms and he realizes the tobacco supports so important to his state will no go through without food stamps."

Stockman, who formerly served in the House, and other Reagan advisers have insisted that the genuinely needy will not be touched by the administration's desire to cut "waste and fraud," but the staff proposal submitted to Stockman would achieve generally across-the-board benefits reductions.

The proposal, obtained by The Washington Post, was prepared by Carlson for Stockman's use in preinaugural economic discussions with Reagan and his top financial advisers.

It could not be learned how many of the elements in the package are under consideration, but OMB examiners this week were reviewing Department of Agriculture food stamp spending data.

According to sources, the nature of the data requested for review suggests that OMB is hewing closely to the lines suggested in the staff proposal.

A saving of $1.3 billion for this fiscal year is envisioned by not requesting a supplemental appropriation that will be needed to keep the program going at present levels through Sept. 30.

The alternative to such a step would be a shutdown of the program for several months -- a political impossibility -- or a reduction of individual benefits to the tune of $1.3 billion.

Acknowledging that such a step would be "politically sensitive," the proposal says the $1.3 billion saving can be achieved only by making a decision this month.

A second, longer-range step, foreseeing a reduction of $2.5 billion in spending, would be applied to the fiscal 1982 budget, when the entire program is expected to cost between $12.3 billion and $12.8 billion.

Generally, the proposal says, major savings could be achieved by counting a poor child's free school lunches against his family's food stamp allowance; tightening eligibility for residents of Puerto Rico, where the program costs about $1 billion a year, and lopping off 2 million mainland participants by stiffening income limits for eligibility.

But the principal fiscal 1982 saving -- about $1.1 billion -- would come by changing the so-called "benefit reduction rate." Benefits now are reduced by 30 cents for each additional dollar earned above the eligibility kimit. The OMB proposal would set the rate at 35 cents per dollar earned.

Critics of this approach, which has been debated at length in the past, argue that it discourages low-income earners and welfare recipients from working and earning more. As their income rises, they are penalized by reduced food stamp allotments.

Another suggestion offered in the proposal would count federal energy assistance, estimated at $1.4 billion in fiscal 1982, as part of a recipient's income. That approach, lifting some participants out of eligibility range, would save $278 million in the fiscal year.

As inflation and recession have helped pump the food stamp program to its current annual spending level of about $11.1 billion, the program has become increasingly controversial.

Popular political rhetoric holds that the program is larded with freeloaders, cheaters, waste and fraud. Changes directed by Congress since 1977 have tightened the program considerably.

Last year, for example, most college students were made ineligible for food stamps. According to USDA's Food and Nutrition Service, 150,000 students were eliminated, leaving only welfare recipients, elderly and disabled students on the rolls.

Changes in 1980 and 1977 eliminated 1.4 million people from the program by tightening eligibility rules. But a liberalizing feature of the 1977 law removed the requirement that a participant pay for part of his or her stamps, which led to a 32 percent increase in elderly participation.

USDA statistics show that more than 80 percent of recipients are dependent children and their parents in single-parent households, while about 13 percent are elderly or disabled.

The bulk of food stamp households are poor -- well below the federal poverty line of $7,450 annual income for a family of four. Average family income is $3,900 and nearly two-thirds of food stamp households own no car or other vehicle.

"The average food stamp user is white and rural -- not black, urban or Hispanic, as many people believe," Richmond said. "I envision no congressional resistance to reducing waste, but there will be strong resistance to any emasculating of the food stamp program."