President Reagan tried to work his personal magic again yesterday, giving House and Senate conferees on the farm bill a pep talk on budget frugality, but he apparently didn't get very far.

The conferees returned to Capitol Hill, convened their first work session to hammer out a new four-year farm package and promptly reached an impasse over dairy support prices.

They decided to set that aside for a while and move to easier matters. Next up were price supports for shorn wool. Sure enough, they reached another impasse and then agreed to call it a day.

Those deadlocks in the first two titles of the bill that will set agricultural policy and program levels reflected the intensity of the farm debate and heavy lobbying efforts that have gone on throughout this year.

The Senate version, adopted under intense White House pressure, is estimated by the Department of Agriculture to carry a five-year cost of $10.6 billion. The House version would cost $16.6 billion, a figure the administration says is unacceptable.

Sen. Jesse Helms (R-N.C.), chairman of the conference, said the president told legislators yesterday that he would support "something in the nature of the Senate bill."

But his counterpart, Rep. E. (Kika) de la Garza (D-Tex.), head of the House conferees, repeated a complaint that the administration has played a sort of numbers game with the budget and has made the House farm bill its scapegoat.

"This morning the president said our bill was $6 billion over the budget, and now I get a letter from him saying it is $8 billion over," de la Garza told the conference. "Here you go again, Mr. President . . . . I wonder if we might just fire all the budget people and do our own thing."

The conferees then tried to do their own thing, but they didn't get very far, sloshing around first in dairy provisions and then getting tangled in the lint of the wool provisions.

As has been the case all year, dairy price supports again became the major stopping point. The House and Senate bills set identical dairy price supports for fiscal 1982, but the House version would cost roughly $600 million more in the later years of the bill, according to the Department of Agriculture.

The House twice rejected efforts during floor debate to trim the dairy program more, and the House conferees stood adamantly yesterday against going any lower.

The Senate conferees showed a little give, agreeing to a compromise offered by Sen. Robert J. Dole (R-Kan.) to adjust support rates slightly in a way that would have added an estimated $100 million to $150 million to the cost of the bill. The House declined the offer, voting 9 to 3 against it.

The administration contends that the program must be cut sharply so that costly government acquisitions of surplus cheese, butter and dry milk can be curbed. The USDA projects a $2 billion price tag for the surplus goods this year.

With an easy solution not in sight on dairy price supports, the conferees moved on to the wool-and-mohair section of the bill.

There, another deadlock ensued. The Senate bill is less generous to sheep producers, whose price support payments come from duties collected on imported wool at no direct cost to consumers.

Sen. John Melcher (D-Mont.), representing a large sheep-raising area, argued for adoption of the House approach, which would extend the existing program's support rates.

Senate Republicans, however, raised questions about program costs, and said they wanted to know more before making a decision. With that and still another deadlock on other wool provisions, the conference quit and agreed to try again today.