The Reagan administration's vision of a brave new world of subsidy-free agriculture, embodied in its dramatic proposal last week at the Geneva trade talks, poses as many questions for U.S. farmers as it does for their overseas competitors.

Reaction here and abroad to the proposal for a 10-year phaseout of farm subsidies and trade barriers ranged from cautious coolness to hostility. And as the meaning of the Reagan plan sinks in, it seems virtually certain to stir a major domestic political debate.

"It will have political sensitivity everywhere," U.S. Trade Representative Clayton K. Yeutter conceded. But, he added, "We believe that a gradual phasing out of these programs will make it possible for folks to adjust... ."

But by telling the world that it was putting all farm-subsidy programs on the negotiating table at talks to revise the General Agreement on Tariffs and Trade (GATT), the administration also was raising questions about the future of some U.S. agricultural support programs that have become entrenched.

Are western farmers, for example, ready to give up the federal irrigation subsidies that have helped make their deserts bloom and their pocketbooks swell, and have enabled them to break into lucrative export markets?

Is America ready to scuttle the vast federally funded university research network that has helped make U.S. farmers the most productive in history?

Or is the country prepared to abandon the time-honored county extension agent system designed to provide farming and educational information to rural families?

Beyond these, in a world free of the trade barriers that U.S. agriculture complains about, could all American farmers compete and survive?

The likely answer in each case is "no," although few agricultural observers in Washington interviewed last week saw much chance of the Reagan plan becoming a reality.

"The average farmer will say he applauds the administration's move, but if we in the grain trade are on an absolutely level playing field, countries like Argentina, Australia and Canada can clean our clocks every day of the year because of their low capital costs and their efficiency," said one longtime lobbyist.

American farm groups reacted dubiously to the administration's proposals. The American Farm Bureau Federation said it would not endorse the package until it saw how far other producer nations would go in curbing their programs. The National Farmers Union and the American Agriculture Movement denounced the plan outright, warning it would lead to a roller coaster of price and supply.

"It is going to be impossible to ever achieve the ideal situation in trade," said AAM's David Senter. "This plan is another statement of this administration's philosophy. They've had difficulty managing our farm programs year to year, let alone a 10-year program like they're proposing now... . I don't think the plan will be taken seriously either here or abroad."

Michael L. Hall of the National Corn Growers Association said the administration is attempting "to force the issue and show the level of subsidization around the world...but I've seen two previous GATT rounds and the levels of expectation always are raised and then not met. It leads to cynicism and disillusionment."

He and Senter noted that the U.S. farm support programs, some of which provide outright subsidies to farmers, have been instrumental in providing a steady food supply at relatively low cost to American consumers. "The public support for an abundant and reliable food supply is large," Hall said.

Others, however, saw the administration proposal as an intentionally overstated gesture to focus more attention on the central issues beleaguering world agricultural trade -- massive overproduction and the growing costs that taxpayers around the world bear in supporting farmers.

U.S. farm support programs last year cost about $26 billion. European Community subsidies to farmers cost at least that much. Japanese barriers to agricultural imports protect farmers there and force consumers to pay far more than the world market price for many commodities.

Experts such as Dennis T. Avery, a State Department agricultural analyst, point out that subsidies by producing countries have spurred overproduction and led the way for protectionist policies that disrupt markets and distort prices.

"The intensified farm trade conflict may actually be good news," Avery said in a recent speech. "It may well precipitate the spontaneous combustion of the farm subsidies of all the affluent nations. Consumers would get a reduction in their cost of eating from more efficient organization of world farm production."

He also said a subsidy meltdown could bring other good news to U.S. farmers. He predicted demand for farm products would go up and high-cost competitors would be deterred. Avery also predicted that a subsidy phaseout could radically cut production costs, make megafarms less efficient and increase the number of U.S. farmers on smaller-sized operations.

Senate Agriculture Committee Chairman Patrick J. Leahy (D-Vt.) added a cautionary note. He warned that he and others on Capitol Hill would not allow the administration to use the GATT negotiations "to push through proposals that have failed in Congress."

Leahy said the administration's proposal "clearly raises the stakes in the complex game of world agricultural trade. What we need to do is see whether other countries put their subsidies on the table. I have faith in the ability of our farmers to compete on the world market. Now we'll see if our trading partners have similar faith in their farmers."

"The proposal is constructive from the point of sparking a debate," said Rep. Dan Glickman (D-Kan.), chairman of the House Agriculture subcommittee on wheat and feed grains.

"The only way to get the attention of the world is to focus on the subsidies and on the restrictions and the cost of programs. Anything short of this would have been a hummer.

"I view the proposals as a good incentive for getting people to the negotiating table. That's the good side... . But we are not going to get rid of the extension service. And I'm not going to let the Europeans interfere with how much money we spend on biotechnology research at Kansas State University. It's not their business," he said.

Glickman, just back from a meeting of the International Wheat Council in London, said the administration proposal caught the attention of delegates from about 100 countries.

"They were taken aback," he said. "They had assumed we would play it incrementally. They feel a growing frustration with subsidies and trade restrictions. We all agreed we need some agreements on market sharing, in order not to break ourselves if nothing else."