Administration efforts to cut costs of a new farm bill suffered another setback yesterday as the Senate narrowly rejected a proposal to further scale down the expensive dairy support program.

By a 50-to-47 vote, the Senate tabled an amendment by Sens. Daniel Patrick Moynihan (D-N.Y.) and Paula Hawkins (R-Fla.) that could have trimmed an additional $600 million from dairy support costs over the next three years.

Yesterday's vote -- the first serious action on the farm bill since Nov. 1 -- was an asterisk to a day that otherwise saw the Senate dig itself into a deeper political-parliamentary mire over the measure.

The impasse involves a freeze of "target price" income supports paid to grain, rice and cotton farmers. The pending bill would freeze the supports at current levels for four years; the administration wants a less costly one-year freeze with reductions in later years.

The chamber earlier rejected a one-year freeze on a close vote. Majority Leader Robert J. Dole (R-Kan.) then offered a variation of that, but, short of votes enough to pass it, he had refused to subject it to a roll call.

Dole's action also blocked Democrats, led by Sen. John Melcher (D-Mont.), from offering an alternative proposal they said would cut the bill's costs by about $8 billion.

The deadlock continued to stir emotions yesterday. Sen. Tom Harkin (D-Iowa), angry over the delays, charged that Dole and other Republicans were "stalling" and "working behind closed doors to cut deals."

Dole retorted that the Democrats were angling for political gain in the 1986 elections, but said he would continue to insist that the Senate produce a bill that would not be vetoed by President Reagan.

"Those who want to have the president veto this can have their way," he said. "My farmers don't care about how many seats are involved in 1986. They're worried about their own."

Dole's amendment was tabled on an 88-to-8 vote last night, clearing the way for him to retain control of the floor and offer yet another compromise that will be debated today. Dole said his new plan would include both a one-year and a four-year income-support freeze, which he called a "multiple choice" to attract more support. House-Senate conferees could then work out a solution, he said.

Dole also said the administration has sent signals that it might accept a bill costing about $50 billion, instead of the three-year $35 billion cost target set by the congressional budget resolution. The administration says the bill now would cost $65 billion.

The Senate's approval of its Agriculture Committee dairy support plan left the bill at sharp odds with the House-passed version, which would create a "diversion" program that would pay farmers to reduce their milk production.

The Senate bill proposes to cut surpluses by lowering the price support from the current $11.60 per hundredweight to $11.10 on Jan. 1, 1987. It would cost about $598 million less than current law.

But Moynihan, Hawkins and Sen. John H. Chafee (R-R.I.) insisted that additional major savings could be achieved by cutting the support rate next Jan. 1, which they said would force farmers to more quickly balance production with demand.

Hawkins said the committee version would require the government to spend more than $2 billion next year to purchase about 17 billion more pounds of surplus milk, butter and cheese for storage in warehouses that she described as already bulging with surpluses.

"Unless the amendment is approved," Chafee said, "the government will buy 10 percent of all the milk produced next year. We now have enough surplus to give every American a two-month supply of butter, a three-month supply of cheese and a two-year supply of milk. This thing clearly is out of control."