WASHINGTON (AP) _ Farm price supports, rural development programs, food stamps and school lunches are big-ticket budget categories where President Reagan hopes to save money in the Agriculture Department.

But some of the fine print bears a closer look. Screwworm control, for example, and the ever-present fire ant. And don't forget USDA's battalion of economists and a pressing need to upgrade their fearless predictions.

Some of what was in Reagan's final budget sent to Congress last week will probably be reworked by the incoming Bush administration, but a lot will be rubber-stamped as is - before Congress has its say.

So far, congressional farm leadership has reacted grumpily to Reagan's USDA budget plans. Rep. Kika de la Garza, chairman of the House Agriculture Committee, D-Texas, said the Reagan spending blueprint probably had been dead for some time before it even got to Capitol Hill.

Overall, the Reagan budget calls for USDA spending in the 1990 fiscal year that will begin on Oct. 1 to be about $42.4 billion, down 19 percent from $52.1 billion this year.

Most of the $9.7 billion in cuts would come from commodity price support operations and various other programs lumped under small community and rural development. A number of other categories would be cut, too, but some would get increases.

Among the department's marketing and inspection programs, for example, the Animal and Plant Health Inspection Service would be able to boost its services to a ''program level'' of $353 million from an estimated $333.8 million this year. The agency's cash outlays, however, would decline to $296 million from $341 million this year.

Program level represents the total financial value of benefits provided to the public, while ''outlays'' are actual spending - the amounts the Treasury pays to carry out various programs.

As used by USDA, program levels include the value of professional services such as research or technical assistance activities, or in-kind benefits such as government-owned commodities.

The agency, APHIS, would hold brucellosis eradication at $55.8 million in the 1990 budget, unchanged from this year. Under this program, the agency works with state, industry organizations and individual livestock herd owners to control and eliminate the disease.

Screwworm control, another APHIS function, also would remain at the current level of $32 million. The control effort is aimed at curbing the screwworm fly, which produces the larvae, or maggot, that injures and sometimes kills cattle, sheep and other warm-blooded animals if not treated.

The 1990 funds would enable APHIS to continue its operations in Mexico and Guatemala to prevent the northward movement of the flies.

Other APHIS activities include programs to control cotton boll weevils, medflies, grasshoppers and fire ants and certain predators, mainly coyotes, that prey on livestock.

An agency that looks out for the welfare of the consuming public is the Food Safety and Inspection Service, which was proposed to operate at a 1990 program level of $424 million, up from an estimated $406 million this year, the same as its outlays.

Inspection at livestock and poultry slaughter plants is expected to account for $242.2 million in 1990, up from $231.6 million this year. Inspection at processing plants would rise to $98.8 million from the current operating level of $96.8 million.

In the Agricultural Marketing Service, regulatory operations would be programmed at $171.1 million, only slightly above this year's $170.8 million. Outlays are expected to rise to $127 million from $113 million this year.

User fees would support 81 percent of the agency's 1990 budget, according to the Reagan plan, including $12.5 million in new user fees to cover postage, printing and handling of tobacco market news reports and several other operations.

Other marketing and inspection agencies include the Federal Grain Inspection Service, the Office of Transportation, Packers and Stockyards Administration and the Agricultural Cooperative Service.

Another USDA group involves economics and statistics, which provide so much of the grist that goes into the making of farm policy, in Congress as well as within the administration.

The outlays for this group would increase to $123 million from this year's spending of $114 million, approximately the combined program levels for two agencies, the Economic Research Service and the National Agricultural Statistics Service.

Department budget officials said the ERS is seeking an additional $2.4 million to collect and analyze data on pesticide and chemical use in agriculture. The NASS wants an increase of $7.4 million to improve crop yield estimates and to upgrade information processing systems in state offices of the agency.

Another category in the budget is ''departmental activities,'' sort of a catch-all item with 1990 spending pegged at $117 million, down from this year's $120 million. Included are operations of the office of the secretary of agriculture, the USDA's inspector general and general counsel, and various administrative offices.

End Adv for Sunday Jan. 15