The morning after President Reagan's State of the Union address, a Republican House member remarked to a colleague that he was immensely relieved at what he had heard. By emphasizing cooperation and bipartisanship, by addressing specifically the concerns of the unemployed, the farmers, women, minorities, students and the elderly, the president "made it a lot easier for me to go home this weekend and say I can support him."

"You better make the speech this weekend," the second GOP member said, "'cause you're going to have trouble making it after January 31."

Tomorrow is the day the Reagan budget formally comes down, the day the broad rhetoric of the State of the Union speech gets put into hard dollars. What the second congressman was saying was that the budget will show little change from the old Reagan priorities of defense first, tax cuts second and domestic spending a distant third.

In that very fundamental sense, there is less to the president's accommodative new tone than meets the ear or eye. But it would probably be a mistake to think that something significant is not taking place. Words have importance for a professional speech-maker like Ronald Reagan, and the words he used in the State of the Union may turn out to be a better clue to where he is headed than all the dollar signs in the budget.

Take defense spending, for example. Reagan gave no indication that he would go beyond the token cuts already outlined by Defense Secretary Caspar Weinberger. The word from the Republican leadership in Congress is that he will not "participate in" cutting the Pentagon any further.

But by saying that "most of the major systems needed for modernizing our defenses are already under way," Reagan has prepared the rationalization for accepting what most Republicans (as well as Democrats) in Congress say is inevitable: a stretchout of the defense spending timetable and a refusal to start any new weapons systems.

Similarly, just as he accepted and praised a Social Security compromise proposal that involves stiffer tax increases than he wanted and less in benefit cuts, so his rhetoric leaves room for backdowns in other areas of the domestic budget. He has reshaped his ambitious 1982 plan for turning back federal programs to the states into a modest block-grant proposal. He has acknowledged the need for some sort of federal jobs program, and almost certainly knows that what Congress will send him will be larger than he asks.

All this is not to suggest that Reagan is ready to roll over and let Congress have its way. He is plainly prepared to fight hard to preserve the 1983 installment of his original three-year tax cut and to resist moves to strip the indexing of tax rates from the law before it takes effect next year.

That poses a direct challenge to the Democrats and to those Republicans on Capitol Hill who see deficits and interest rates as far more of a threat to sustained recovery than the removal of a tax break that polls show most Americans would willingly forsake.

Reagan's acknowledgment that tax increases will likely be necessary later in the decade to keep the deficits from climbing back up to the current year's staggering $200 billion level will fuel the opposition to the current tax cuts.

Another area where he is challenging the growing sentiment in Congress is the issue of trade. Nothing was more striking in the State of the Union than Reagan's statement that "America must be an unrelenting advocate of free trade." Not "fair trade," or "open trade," but "free trade," the classic phrase. And to underline the point, the president said: "As some nations are tempted to turn to protectionism, our strategy cannot be to follow them but to lead the way to freer trade."

This is a clear defiance of the House vote in the lame-duck session for protectionist "domestic-content" legislation on autos, and the efforts in both chambers to impose "buy-American" amendments on government programs.

It is part of Reagan's insistence, in both public speeches and private meetings, that government policy must assist--and not resist--the "great transition" of the American manufacturing base from heavy industry to high technology. And it comes at a time when the Democratic Party and most of its leading presidential hopefuls are lashing themselves ever more tightly to the very protectionist measures Reagan has rejected.

Here we have the makings of a great political-economic debate--and one on which Reagan is clearly on the side of change. However resistant he may be on other fronts, here he is clearly on the offensive, moving with history and not against it.