Congressional conferees yesterday stirred up a milk price support concoction that wasn't quite cream, but wasn't quite skim, either, and may taste sour down at the White House.

After several difficult days, the farm bill conferees finally agreed on a dairy support plan that in effect split the difference between House and Senate versions.

The plan would cost an estimated $3.175 billion through fiscal 1985, about $151 million more than the Senate version the administration supported in its effort to prevent costly purchases of surplus milk.

Department of Agriculture officials were not pleased with the outcome, but it was clear from the jangling tone of the debate that the conferees would move no more.

The debate touched on such topics as the president's hard line on cutting dairy support costs, the role of Office of Management and Budget Director David A. Stockman, the Constitution, the great American milk cow and the vanishing family farm.

But in another way it was just as Rep. James M. Jeffords (R-Vt.) put it: "We're playing a game here is what it amounts to."

The game involved numbers--dollars, poundages, parity levels, hazy estimates of future costs, herd sizes--and on that score little was certain.

Rep. Tom Harkin (D-Iowa), leader of the campaign to prevent further cuts in the program, called yesterday's agreement a victory for dairy farmers because it retained a floor for milk price supports at no less than 70 percent of parity.

The administration and its allies had argued for a formula that would allow the support level to drop below that if government surplus acquisitions went above certain figures.

"The signal to dairy farmers is now in the bill," Harkin said afterward. "They must reduce production, but parity can go back to its historic 75 percent level if they achieve the goals that are set."

The conferees also agreed yesterday to eliminate a price support program for sunflowers that had been in the House bill, and agreed on target prices for rice that would cost about $140 million, some $24 million more than the Senate approach but $710 million less than the House wanted.

The dairy compromise engineered by Sen. Robert J. Dole (R-Kan.) would keep support prices at $13.10 per hundredweight through fiscal 1982, then peg them at 70 percent of parity in future years.

But if anticipated federal surplus acquisitions were less than 2.69 billion pounds in fiscal 1985, the parity level would move to 75 percent, which would amount to $18.63 per hundredweight at today's rates.

The price also could be moved to 75 percent of parity if surplus purchases were less than four billion pounds in fiscal 1983 or 3.5 billion pounds in fiscal 1984.

The meaning of those numbers is that dairy herds will have to be reduced substantially if farmers expect to see their price supports increase. USDA projects surplus purchases this fiscal year of 8.6 billion pounds of butter, cheese and nonfat dry milk.

A central element in the milk fight was the administration's insistence that the conferees adopt the Senate approach to controlling the program. The House delegation, however, refused to budge during hours of dispute, and Rep. E. (Kika) de la Garza (D-Tex.), chairman of the House Agriculture Committee, made it plain that something more was at stake.

He said the conferees had compromised on a number of issues, heeding President Reagan's appeals, but "there comes a time when we have to realize the co-equal aspects of the branches of government."