WHAT IF President Reagan interprets his expected landslide victory Tuesday as a mandate to expand the radical political, economic and social initiatives sometimes called the "Reagan revolution?"

To be sure, that isn't the way this election has been cast up to now. Reagan has revealed very little to the American public about his plans for a second term. His campaign has relied on imagery and rhetoric, and has provided few insights into his agenda for the future.

So the impression has emerged that the next four years could be fairly dull ones, in which the president wrestles with increasingly intractable economic problems or attempts to get a few minor reforms past entrenched interest groups and a divided Congress.

Yet that is not the way the future is seen by the New Right political thinkers and supply-side economists who make up the core of the conservative movement in Congress and the academic think tanks. They acknowledge that some of the fire and excitement has gone out of the crusade begun in 1981, but they are convinced that Reagan ultimately will adopt their agenda if re-elected.

"Reagan is teetering between FDR and Woodrow Wilson," says Rep. Newt Gingrich (R-Ga.), a leading member of the Conservative Opportunity Society (COS), a small group of Republican activists in the House of Representatives. "There hasn't yet been a transition to a new governing system. That's why we must keep the Democrats off balance in the next two years with new ideas."

For all the murkiness of the Reagan administration's plans, there is little mystery about what the militants of the conservative movement want. To find out, it is only necessary to consult members of the COS, or the Heritage Foundation or refer to the 1984 Republican Platform.

Consider, for example, agriculture -- a sector of the economy that has been subsidized by price supports, tax concessions and government credits for half a century -- more than $18 billion worth in 1983. Supply-side conservatives want to end, or at least sharply limit these subsidies. They argue that modern farming is just another business and should face the same free-market risks as others.

Price supports and other subsidies, contends North Carolina State Prof. E. C. Pastour Jr. in a paper for the Heritage Foundation, is disguised "income redistribution." He prefers policies that would result in a radical transformation of rural America.

A key word of the conservatives is "privatization." Under plans already drawn up or proposed, numerous functions now performed by the government (such as insuring bank deposits and controlling air traffic) would be transferred to the private sector. One idea would be to end the federal government's monopoly of mail boxes and mail slots, so that private mail services could have access to them. Another idea, already being tested in several cities, would result in the government's turning over the management or ownership of public housing projects to tenants and tenant associations.

Also targeted for change is the welfare system, which conservatives say promotes illegitimate births and shiftlessness among poor people. Under study in the Reagan administration is a plan that would, in effect, shift some of the costs of caring for illegitimate babies from taxpayers to families that want to adopt children. Some argue this could be done by cutting aid for dependent children (welfare), reducing federal funding of foster homes and facilitating adoption of babies by private individuals.

Perhaps the most controversial conservative idea of all involves imposing strict new limits on the Federal Reserve Board's freedom to regulate the money supply. The Republican Party platform adopted in August states that "the Gold Standard may be a useful mechanism for realizing the Federal Reserve's determination to adopt monetary policies needed to sustain price stability." A less radical alternative has been advanced by Richard W. Rahn, chief economist for the U.S. Chamber of Commerce. This would link the growth of the money supply to fluctuations in the price of a "basket" of commodities traded in international markets.

New light will be shed on the details of the conservative agenda on Dec. 7, when 1,200 proposals drawn up by 150 scholars, businessmen and specialists is unveiled by the Heritage Foundation, the conservative Washington think tank whose annual operating budget now exceeds that of the older, more liberal Brookings Institution. The title of the document will be "Mandate 2."

According to Gingrich, the aim of conservative polticians and intellectuals is an ambitious one: "to change the structure (of the country) from a welfare state to an opportunity society."

"We must transform the federal government to make it more like Sears, Roebuck or American Express," says the congressman.

In Gingrich's view, that transformation is yet to occur. "We (the Republicans) have been a Grand Old Party, but that hasn't made us a majority party." Only radical reform that broadens the party's base sufficiently to give it control of the House of Representatives will accomplish that, he contends.

Although the agenda of conservative activists such as Gingrich is traditional in some respects -- they oppose most liberal-era social programs -- it also contains elements that could, possibly, appeal to "yuppies" and populists as well.

Gingrich's new book, "Window of Opportunity," extols high-tech industries, attacks the "elites" that control the Department of Defense, the legal profession and the education establishment, and declares that "we must be very cautious about where and when we commit ourselves economically and militarily."

Gingrich, who received a Ph.D. in modern European history from Tulane University, says his views have not only been shaped by such conservatives as Rep. Jack Kemp (R- N.Y.), but also by futurist Alvin Toffler (author of "Future Shock" and "The Third Wave").

The Conservative Opportunity Society, chaired by Rep. Vin Weber (R-Minn.), is an example of the New Right's efforts to establish intellectual momentum and cohesion -- something neither Democrats nor Republican moderates have been able to do in recent years. It serves as a clearinghouse of ideas that are "politically futuristic," in the words of a congressional aide, while keeping its lines out to groups such as the Heritage Foundation and the American Enterprise Institute, and to other groups in Congress, such as the Military Reform Caucus.

On matters affecting high-tech industries, COS members have worked with the Task Force on High Technology Initiatives of the Republican Research Committee, which was instrumental in passing legislation favorable to high-tech companies.

Whether conservative activists will be able to push through their agenda in a second Reagan term is, of course, an open question. It will depend in part on the results of the congressional elections and the state of the economy. But it will also require winning over or neutralizing Republican moderates in both Congress and the administration.

A good example of the problem they face can be seen in agriculture. While conservatives may like the idea of eliminating costly farm price- support programs, the opposition looks forbidding. Recently appointed the top White House adviser on food and agriculture is John D. Gordley, former legislative assistant to Sen. Robert Dole (R-Kan.), a powerful advocate of farmers.

There may be more receptivity to the conservative agenda in the area of taxes. The "tax simplification" plan that the Treasury Department will soon unveil is reported to contain a number of elements satisfactory to supply-side conservatives. According to one source, the proposal would reduce the top personal tax rate from 50 percent to 35 percent, in return for closing dozens of loopholes and ending numerous deductions. Conservatives are pressing for an increase in the current $1,000 tax deduction for dependent children as a way of appealing to low-income constituents.

Stiff opposition is expected to tax reform, but conservative activists such as Gingrich recall that skeptics have been repeatedly surprised.

"The people who are skeptical now are the same ones who said we couldn't get a crime bill through Congress, that we couldn't get an immigration bill out of the House and that we couldn't get control of the (Republican Party) platform," he says.

"Even if the White House is lethargic -- and I don't think it will be -- you are going to see various groups lighting a fire under them," said Burt Pines, the Heritage Foundation's vice president for research.