The Senate approved a farm bill yesterday that carries no major changes in agricultural support programs but breaks new ground in environmental protection in setting the nation's agricultural policy for the next five years.

The 70 to 21 vote came late in the afternoon, following compromise on scores of amendments that had bogged down the Senate for days.

Floor managers cautioned their colleagues that ongoing budget negotiations with the White House would inevitably mean changes in the planned spending of $54 billion over the next five years, spending that must be done through annual appropriations bills.

The House is near passage of its version of the farm bill, and a conference between the two houses will negotiate a single bill to be sent to the White House, where President Bush is expected to get veto recommendations from agencies concerned that the bill costs too much.

Agriculture Committee Chairman Patrick J. Leahy (D-Vt.), who pushed for many of the environmental changes, said the bill "is the most progressive farm bill I've seen since I've been here. . . It is an environmentally conscious farm bill. It is one that allows us to do the things Americans want."

Among the environmental breakthroughs in the bill is a ban on the export of agricultural chemicals illegal in the United States. The bill also establishes standards for use of the phrase "organically grown" and lays down new policies designed to protect wetlands and forests.

The Agriculture Committee's ranking Republican, Sen. Richard G. Lugar (Ind.), said changes in the bill may be necessary once budget negotiations are completed with the White House. "We feel that agriculture should pay its share," he said.

Minority Leader Robert J. Dole (R-Kan.), who also is a member of the Agriculture Committee, said, "For the most part we are proceeding with the philosophy we put together in 1985," as the White House and congressional leaders planned all along. But he added: "The problem with the 1985 farm bill was that it cost about $80 billion in program outlays. We no longer have $80 billion to spend."

Before recessing for the weekend, the House fought off an effort to eliminate government subsidies to honey producers. The Senate earlier in the week cut the subsidies from its bill.

The Senate, in the space of an hour, cut 23 amendments from a list of 40 ranging from red tape reduction to wetlands conservation.

The bill establishes price-support programs for commodities and sets policy for nutrition programs, agricultural exports, soil and water conservation, agricultural research and extension work, food inspection and other responsibilities of the Agriculture Department.

The administration's chief concern clearly was budgetary. Secretary of Agriculture Clayton Yeutter and the Office of Management and Budget said they would recommend a veto if the cost of the bill were not decreased.