After weeks of intense negotiation and political gamesmanship, the Senate Agriculture Committee took a small but important step yesterday toward breaking a logjam over the shape of a new federal farm-support program.

In effect, the committee decided to agree on the shape of a table -- that is, which of a number of pending proposals would be used as the "vehicle" for marking up the key price-support section of a 1985 farm bill.

But even at that, the committee was nearly as indecisive as it has been for weeks, caught in the painful vise of wanting to maintain income supports for farmers while holding down soaring federal farm costs.

The panel, after voting down a proposal by Sen. Tom Harkin (D-Iowa) that called for mandatory production controls, approved two other measures as the road map for proceeding.

Chairman Jesse Helms (R-N.C.) ruled that the committee would use a bill introduced by Sens. Edward Zorinsky (D-Neb.) and Robert J. Dole (R-Kan.), since it got a larger majority than another offered by Sens. Thad Cochran (R-Miss.), Mark Andrews (R-N.D.) and John Melcher (D-Mont.).

Helms' ruling drew several protests and the chairman conceded that "what I did was novel."

Sen. Alan J. Dixon (D-Ill.) asked for reconsideration of the vote, but the debate had gone on so long and attention spans were so altered that finally he dropped the request.

The Zorinsky-Dole proposal calls for lower price support loan rates on basic commodities and would continue direct subsidy payments to farmers, although at lower levels than current law provides.

But Helms assured committee members that the Zorinsky-Dole plan would be subject to amendment throughout. And Majority Leader Dole, who orchestrated a series of closed-door meetings over the past 10 days in an attempt to break the impasse, indicated that an entirely new package most likely would emerge.

The committee appeared to be edging cautiously toward the Cochran-Andrews-Melcher approach, an untested "marketing loan" idea that would replace the current price support and target price subsidy payment schemes.

Under this approach, farmers could get federal crop loans at predetermined rates and then pay back only the amount for which their commodity actually sold.

If corn, for example, sold for $2 per bushel and the loan was for $3, as the bill proposes, the farmer would keep $1 and pay back only $2.

Supporters argue that this approach would reduce federal surplus acquisition costs, discourage overproduction and allow American grains to reach "market clearing" prices that would make them more competitive in the export trade.

Although the committee has been stalled for weeks, in part because of budget-busting fears, Andrews and others made it clear yesterday that propping up the sagging farm economy through the new farm legislation has become the No. 1 political goal.

"Let's not worry about budget figures," Andrews told reporters who questioned the cost of his proposal. "They've got their own problems . . . . We didn't build this to fit within the budget. We built it as a solid farm program."

He, Melcher and Harkin, reflecting committee-wide sentiment, made another point clear. "Nobody wants to reduce farm income," Harkin said. "I won't support any proposal that would bring this about."

Another key factor hanging over the committee, increasingly apparent as the impasse has intensified in recent days, involves senatorial pride of authorship -- that is, who will get the credit for producing the magic solution to pump profit back into agriculture.

Zorinsky at one point, only in half jest, underscored the problem.

He offered to rename his proposal the Dixon bill "because I don't know if there is any positive political gain to be made from having your name on a turkey of a farm bill."