The Republican-controlled Senate Agriculture Committee turned its back on the White House yesterday and approved a dairy program that could exceed President Reagan's spending plans by at least $1.4 billion over the next four years.

The committee vote came as Congress was preparing, in its first budget resolution, to approve the president's spending plans in the abstract. But it may be a sign of rockier times to come as congressional committees turn from broad budget goals to the grit of specific implementing legislation.

The four-year farm bill is the first such legislation to arise this year. The farm-dominated Senate Agriculture Committee, whose chairman is conservative Jesse A. Helms (R-N.C.) began drafting its version yesterday. The House Agriculture Committee will start final work on its version Thursday.

The pro-dairy vote yesterday came just a month after Congress went along with the president and canceled a costly milk price support increase that was to take effect April 1. Dairy industry officials, largely resigned to losing that first time around, ahd concentrated on holding ground in the four-year program.

Their effort found broad-based sympathy at the Senate committee, where GOP members joined Democrats in rejecting the administration's pleas for a much more austere dairy program aimed at reducing federal expenses. p

Only a warning from Sen. Bob Dole (R-Kan.), chairman of the Finance Committee, who said "it won't take many votes to break the bank," seemed to dissuade the agriculture panel from being even more generous with dairy farmers.

Sens. Mark Andrews (R-N.D.) and Rudy Boschwitz (R-Minn.), representing farm states, argued that the administration's proposals for the dairy program dealt inadequately with production cost problems encountered by farmers.

After lengthy debate -- in which the word "consumer" was not mentioned once -- the committee adopted a proposal by Sen. Walter (Dee) Huddleston (D-Ky.) to continue milk price supports at 75 percent of parity after Oct. 1, with support levels to rise if government purchases of surplus milk fall.

"It gives some assurance that supply will be adequate. At the same time, it takes into account excessive production," Huddleston said.

His amendment, according to Department of Agriculture estimates, would cost the government $4.1 billion through 1986. The administration approach, basing supports on 70 percent of parity, would have cost $2.7 billion by the same calculations. Parity is figured by using a pre-World War I index of farm prices and costs.

The administration also was rebuffed in its effort to make price support adjustments in the dairy program only once a year, instead of twice annually as is now the case. The committee version would adjust prices twice a year, with language added by Dole requiring that support prices stay at least at 70 percent of parity. The Dole amendment, it was agreed, could add an additional $100 million cost to the dairy program.

Agriculture Secretary John R. Block, in a message to the committee yesterday, reiterated administration opposition to all bills other than its own and said the administration is unwilling "to accept any amendments to its bill." And Agriculture Department economist William Lesher cautioned that additional costs will jeopardize the milk support program in the long run.

Helms indicated that the panel could reconsider its dairy action, but left only a slim chance of doing so. Helms said he hopes to complete the lengthy bill, involving many other basic commoditie4s, by Saturday.