When it became apparent last week that Sen. Jesse Helms (R-N.C.) would soon be chairman of the Senate Agriculture Committee, the sensitive livestock futures market dipped inexplicably.

Some analysts, maybe jesting, maybe not, suggested Helms was the cause. The reasoning: meat demand would fall if he were able to cut back the food stamp program as much as he has threatened to.

Traders may be hyper-reactive to these things, but there is no mistaking Helms' feelings. His rise to the chairmanship in January will mean the $11.8 billion food stamp program is in for some tough sledding.

The program, administered by the Department of Agriculture and overseen by the committee, will be up for renewal next year. Helms already is eyeing the possibility of cutting it in half.

Speaking for Helms, his chief farm adviser, George Dunlop, said, "Four years ago, the food stamp budget was $5.7 billion. Part of the increase is inflation, but we feel the Carter administration has deliberately mismanaged the program to redistribute as much income as possible."

He added, "We need to see what can be done to stop the massive growth and restore it to a nutrition program . . . for now we have the votes and we think we can do it."

Helms wants to reinstitute a requirement that recipients pay for part of their stamps. He supports tighter eligibility rules. He also wants to deduct a child's free school lunch from a family's stamp allotment.

As Helms and the new Republican majority take over the Senate, they will have both the forum and much of the power they need to put the brakes on the social programs that are anathema to the conservative right.

But in areas such as food stamps, for example, there is another reality. Republican forces like Sen. Bob Dole of Kansas, a leading agriculture figure, and Democrats will have to be contended with. Dole has played a role in keeping the wolves from the food stamp door.

"Helms has offered any number of amendments trying to gut the food stamp program," said Carol Tucker Foreman, the assistant secretary of agriculture who shepherds the program. "I think he'll do more as chairman."

Helms has not been available since the election to comment on directions he will take as chairman. But his record and the views of people who watch him give some pretty clear indications.

The first thing to know about Helms, 59, a former newspaper city editor and television broadcaster, is that he comes from a farm state -- a leader in tobacco, peanut, poultry and eggs, pickles, pork and wheat production.

The second thing is that Helms is an archconservative, a darling of the New Right who regularly rails at big government, bureaucracy and federal giveaways.

Yet, since his election in 1972, he has gone right along with the federal support programs that his farm constitutents like and need. He wants to be tough with the Soviet Union, but, like President-elect Reagan, he opposes the Carter administration's grain embargo against the Russians.

On the Agriculture Committee, that is par for the course. When it comes to standing up for the farmer, committee liberals and conservatives close ranks and usually act as one.

Helms will take charge of that kind of committee in January. One of its early tasks will be extension of the basic farm commodity legislation, a delicate mix of price supports, reserves, set-asides and crop and disaster insurance, all aimed at shoring up U.S. agriculture.

"That is consensus legislation," said Dunlop, who is likely to become chief of the committee staff and who is part of the Reagan transition task force on agriculture.

"We don't see a lot of change coming in that law," he said, "but we feel there will be an increased emphasis by Congress on farm export growth. Congress was cranking up to do that anyway.

"We support diversity -- large, medium and small farms -- and we want to get the committee looking at some other issues, such as forestry, federal lands, soil and water conservation."

Generally, however, conservative Helms is viewed warmly by the big agribusiness firms and large-scale farmers; coolly, by the smaller farm groups, such as the National Farmers Union, which found him voting "right" on only four of 34 key legislative issues in the 96th Congress.

If slogans and catch phrases mean anything, try this. Jesse Helms gathered fame as a broadcaster in North Carlina, billed as "The Voice of Free Enterprise."