OKAY, BUD SHUSTER. In your eight years in Congress, you have shown an ardor to cut the federal budget matched by few people. In your mountain district in central Pennsylvania, Ronald Reagan can fairly be called a hero. Now you and your constituents are seeing your fondest dreams come true.

Only there's a catch. Your foundest dreams, it turns out, include the elimination of federal subsidies for Conrail, the propped-up corporation that subsidizes the Altoona car shope, the largest employer in your district. No more Conrail could mean 6,500 people out of work.

Do you want to reconsider?

How about you, Time Incorporated? You've just this week devoted major portions of all seven of your magazines -- including the cover of Time -- to the stirring theme of "American Renewal," with the implication that President Reagan can bring it about.

Now it appears that Reagan's version of American renewal includes the elimination of postal subsidies, a series of little goodies that your Washington representatives have gone around for years calling the staff of Life, and Fortune too. How do you like the new America?

And you, Frank Wolf. In November you upset Democrtatic Rep. Joseph Fisher of Arlington, and you have to admit you sang the siren song of less government spending a little during your campaign. Less government now turns out to mean a panoply of disasters for your district, including cuts in federal pay rates, school aid, federal pensions and the subway system.

And you too, Robert Kasten and Jack Fields. Both of you unseated prominent liberal Democrats -- Gaylord Nelson and Bob Eckhardt, respectively -- by running against big government. Now you've got your wish: cuts in dairy price supports for you, Sen. Kasten, and new fees for users of the Houston Ship Channel and Houston Intercontinental Airport, to name two of the monuments of your district, Congressman Fields.

And let's not forget you either, American Petroleum Institute. One would be hard put to find a stauncher defender of the free enterprise system than you, especially where oil price controls are concerned, but now you have to swallow cuts in you beloved synthetic fuels program. A bitter pill, isn't it.?

This little game could be spun out forever, but the point of it is that conservatives now have to confront the real world of politics, and decide how conservative they really are. As a theoretical proposition, major cuts in the federal budget would sail through Congress. Republicans are in the majority in the Senate. Self-described "conservatives" are in the majority in the House. It is the rare member who didn't run last fall on the platform that there's too much federal spending, too many government programs, too much budget debt.

All of a sudden, however, major cuts in the federal budget are no longer a theoretical proposition, and tucked away somewhere in the ones President Reagan has proposed is some item or other that will bring tears to the eyes of even the most ardent supporter of the Balanced Budget Amendment. So the question now facing the pro-cuts majority is: Which do you want more, to save your own program or cut everyone else's? Does your own suffering bring on a wave of empathy for the suffering of the guy sitting next to you? Now that your own ox is being gored, do you still want to gore everybody else's?

These are, by the way, questions that old-fashioned liberals need not address. Politically, there are no liberals in Congress with a vested interest in and stated commitment to Reaganism. Philosophically, liberals have never advocated major cuts in anything but the defense budget. And as far as Reagan's program goes, there is an honest and principled case against it.

It runs roughly like this: While conservatives insist that government welfare programs make their beneficiaries dependent on government and thus actually hurt them, liberals say that isn't so. The programs perform the compassionate function they're supposed to. Welfare helps people, and more welfare helps them more. Besides, liberals say, spending on welfare programs has nothing to do with causing the inflation that bedevils everyone else.

So for the liberal minority to oppose the Reagan program not only has little bearing on the program's fate; it doesn't bear the taint of hypocrisy either. Liberals can keep worring about how to win elections. They're off the hook on this one.

But the people who have looked askance at federal spending -- conservatives and moderates in Congress and almost every business lobby -- do have to shoulder the burden Reagan has dropped on them, not just politically but morally too, because there is no easily discernable way to oppose the economic program on conservative principle. They are the people on the griddle.

What they're saying so far is interesting, because sentiment seems to divide cleanly between members of Congress and lobbyists. Conservative members, well aware of Reagan's popularity and of the hostility to government back home, are saying they'll back the program, including the parts that hurt them, up to a point -- the point where the euphoria dies and a goodie-saving stampede starts. Lobbyists are definitely not saying that. If the program means they'll lose their own subsidy, then they won't back the program. That being the case, we will soon find out how powerful lobbyists really are.

Listen to a few congressmen and senators, sounding anywhere from euphoric to stoical:

Rep. Bud Shuster, he of the Conrail-supported factory: "The president has taken the first major step in fulfilling the mandate given him -- and the Congress -- by the American people last November; now it's up to Congress to take the second step by supporting, quickly, the exciting program of fiscal integrity and general national security which he has so courageously set down." No mention of the railroad shops there.

Rep. Frank Wolf, he of the district full of federal employes: "Basically I think I support what the president is trying to do and I think the overwhelming majority of congressmen do. But sure, I guess there are some cuts I'm not sure about." He's a little shaky, but he's still on them.

Sen. Robert Kasten, the man from the dairy state: "Our people are sick of government glut, and are ready to swallow some pretty strong medicine. Now we have the first taste. It's not very pleasant but the important thing is that everyone is getting the same treatment."

Rep. Jack Fields, of the new user fees: "They're part of the beauty of this program. It truly does affect every person. And that's where my excitement is." But an aide adds, "Once people start copping out, there'll be a wholesale run on the bank."

In practical terms, the more of the program the Reagan administration can stuff into one vote -- like a "reconciliation" vote on the 1982 budget -- the more likely these men will be to go along. They probably will go along. But if it's 50 bills stretching out over a period of months, they'll go along only with what hurts the other guy.

Now listen to some lobbyists, sounding wary and tough:

John Steele, vice president of governmental affairs of Time Inc., the man with the postal subsidies: "Quite frankly, no comment. Haven't read it yet." No help for the president there.

Charles DiBona, president of the American Petroleum Institute: "In a time of national security need caused today by our heavy reliance on imported oil from insecure foreign sources there can be an appropriate government role in encouraging synthetic fuels development. The appropriate levals and methods of government involvement need careful review." No help there, either.

Bill Jackman, assistant vice president, the Air Transport Association: "I think we really haven't focused on the whole program. We've focused on our part. The administration might have to give a little in the Senate Commerce Committee. That's the way it usually works."

Patrick Healy, secretary, the National Milk Producers Association: "The president didn't address dairy price suupports in his message to Congress. That leads me to believe they do not have a proposal carved in granite and will look at our proposal. Secretary Block and I are both reasonable men dedicated to the porvision of an adequate supply of food and we will get together."

For the most part the lobbyists want to break the program up and get it into the committees they're comfortable with. Already, last week, before the wheeling and dealing had really begun, they were crowding every available briefing and hearing room, armed with concerned expressions and yellow legal pads. They were not anxious to take their medicine.

We have heard an awful lot lately about how liberalism has run out of ideas, turned stale, become an ideology dedicated to government by buy-off. We've heard a lot about how the free enterprise system must be allowed to function, and how government must be cut back. Now we get to see whether the people who have been saying all this stuff really believe it. The budget cuts are a pretty fair test of the sincerity of Washington conservatism. If conservatives turn out really to be conservative only where the other fellow is concerned, then it's fair to ask whether those bold, stirring new ideas of theirs are anything but a lot of self-interested talk.