WASHINGTON - President Clinton quietly and reluctantly signed historic farm legislation yesterday that snaps the decades-old link between crop prices and government subsidies.

Although the law lifts many government controls on farmers, it ''fails to provide an adequate safety net,'' the president said from a White House mourning the death of Commerce Secretary Ron Brown.

Clinton opposed the key farm provisions but said growers need to know what the government has in mind for them as they head to the fields this spring. Agriculture Secretary Dan Glickman pledged the department would do everything in its power to carry out the law.

The law ends government-guaranteed prices for corn, other feed grains, cotton, rice and wheat - a staple of U.S. farm policy since the Depression. Instead, farmers will get guaranteed payments that decline over seven years and an immediate end to most planting controls. The payments total $36 billion over seven years and account for most of the spending in the $47 billion law.

''This farm bill is the most historic change in American agriculture since the 1930s,'' said Sen. Richard Lugar, R-Ind., chairman of the Senate Agriculture Committee. ''Production and supply controls will end, and farmers will produce for the market for the first time since the Great Depression.''

The administration opposed the bill because it gives farmers a windfall of high payments when skyrocketing market prices mean traditional subsidies would have fallen sharply. Afterward, the guaranteed payments dwindle, giving growers little protection if prices collapse.

Clinton said he would propose legislation next year to restore the safety net. Congress will definitely get a shot at crafting new farm legislation when the law expires in seven years.

Supporters of the new law say the guaranteed payments would put financial planning and risk management into the hands of farmers while guaranteeing farm programs against almost certain cuts in the future.

''With one signature on the market transition contract, farmers will be free from seven years of paperwork and long lines at the county USDA office,'' said Rep. Pat Roberts, R-Kan., chairman of the House Agriculture Committee and chief author of the plan.

Glickman said the department will work on creating tools for farmers to find alternatives, such as revenue insurance, to traditional subsidies. He also said he would urge farmers and bankers to work on ways for farmers to save their payments for a rainy day.

Although the administration opposed the core provision, the bill held enough sweeteners to avoid a veto, including money for conservation and environmental protection and for rural development and research, and a guarantee that food stamps and other nutrition programs will continue while Congress works on overhaul the welfare system.

The administration also supported crop provisions giving growers more flexibility to plant what they want.

Clinton's approval means Agriculture Department employees will rush to carry out a law that guarantees many will lose their jobs with the simplification of farm programs. But Glickman said the law creates enough work to prevent job losses in the first year or two.

Because of an earlier reorganization, the department already expected to lose 2,500 county-level employees between 1993 and 1999. The farm law could increase that number by 1,400, the department said last month.