Intensive lobbying by some of the country's largest irrigation farmers produced a bumper harvest yesterday as the Senate rejected efforts to limit their federal water subsidy.

By 58 to 39, the Senate tabled an amendment that would have curbed the amount of subsidized water that big farms, mostly in California, could receive under federal reclamation law.

The vote came as debate began on a controversial bill that would, in effect, legitimize violations of acreage limits set by the reclamation law of 1902.

Unless Congress revises the law this year, the Interior Department will be required to follow a court order directing strict enforcement of the law, which sets a limit of 160 acres of irrigated water per farmer.

Although about 96 percent of farms using federally provided water in 17 western states are in compliance, a handful of large operators would forfeit their use of cheap federal water.

Most of the argument that has entangled the Senate for months is about the future of those sizable operations--how large a subsidy they should receive, how much more they would have to pay for water.

But as the debate evolved yesterday, the Senate came out foursquare against serfdom.

Which is to say that the subsidy-reducing amendment by William Proxmire (D-Wis.) and Richard G. Lugar (R-Ind.) was tabled, leaving intact an Energy Committee plan to permit as many as 2,080 acres of subsidized irrigation land per farm.

Proxmire called the bill just about every name in the book: "welfare for the richest . . . an unconscionable raid on the Treasury . . . bail-out for the wealthiest."

Lugar, protesting that the bill's generosity was an affront to other farmers whose federal aid has been reduced, termed the amendment an attempt to bring "equity and fairness to federal water policies."

Their amendment would have continued delivery of water at less than cost but would have required partial to full repayment according to farm size. Farms larger than 960 acres would have to repay the subsidy in full.

Western senators, who had described the proposal as radical, washed it away with an avalanche of denunciation.

Malcolm Wallop (R-Wyo.) repeatedly warned that the amendment would create "a new class of agricultural serfs," presumably the oil and agribusiness firms that operate the largest irrigated farms.

He said the Lugar-Proxmire proposal was an attempt to create new "class distinctions" and to penalize successful western farmers.

"Our amendment is not vindictive," Lugar said. "At best, it is a modest reform. The point at issue is the degree of subsidy."

But Wallop and his allies were ahead of Lugar on that one. Earlier, Wallop had unveiled a list of federally subsidized small watershed projects in Indiana, Wisconsin and other midwestern states.

"It's all right to subsidize midwestern farmers to remove water from their land, and it is grossly unfair to let western farmers put water on their land and pay 14 percent interest on their debt," he said sardonically.

Before recessing last night, the Senate also tabled a modified Proxmire amendment that would have required full subsidy repayment only on farms larger than 960 acres.

Earlier, on a 58 to 39 vote, the Senate refused to require competitive bidding on all federal onshore oil and gas leases.