Sen. Pete V. Domenici of New Mexico transformed himself into a momentary Capitol Hill folk hero July 3 when he lectured budget director David Stockman on Senate "prerogatives," but he also exposed a serious threat to Ronald Reagan's radical economic program.

Raged and Reagan strategist: "How can you worry about Senate prerogatives when so much is at stake?" Domenici was conducting business as usual as chairman of the Senate Budget Committee when he turned down Stockman's request that the Republican Senate accept the spending "reconciliation" resolution passed by the Democratic House.

Domenici is not unique. It was also business as usual the same week with such Republican worthies as Rep. Bob Michel of Illinois and Sen. Bob Dole of Kansas. Indeed, traces of the same syndrome were detectable high within the Reagan administration.

That creates this paradox: While President Reagan's daring initiatives have galvanized the nation and the world, his program is losing momentum. Reagan himself may be too isolated from the process to appreciate, much less reverse, what is happening.

Nothing better illustrates this process than Stockman's failure to circumvent the tedious Senate-House conference committee on the spending resolution by getting Senate acceptance of the Hose version. His comeuppance was widely celebrated in Washington, where the 34-year-old budget director has collected enemies as the often-abrasive foe of business-as-usual.

But far more than Stockman's personal prestige was at stake. At the worst, protracted consideration of the resolution conceivable might reopen the entire spending issue; at best, it detracts from the administration's concentration on its beleaguered tax bill. No mere Stockman brainstorm the shortcut was administration policy approved by the president.

As such, it was supported by Senate Majority Leader Howard Baker, whose steadfast backing of the president's program (even portions he personally questiones) has been a most pleasant surprise to the White House. Support also came from Rep. Trent Lott of Mississippi, the House Republican whip and a tenacious Reaganite.

They found themselves alone. Michel, the amiable House Republican leader, came down on Domenici's side in behalf of the regular order. From the start, Domenici at the Budget Committee has been reluctant to sacrifice his own inclinations and prestige to further the Reagan program.

At the Finance Committee, Chairman Dole has been less obvious than Domenici -- but more difficult. Business lobbyists flatter Dole, saying his stewardship of the tax billmaking him the greatest finance chairman of the age and Reagan's salvation. In truth, the administration got help from the sardonic Kansan only by applying tender, loving and constant care.

Dole last week very nearly negated his substantial accomplishments when he substantial accomplishments when he suddenly suggested a tax "compromise" that would skew rate reductions to benefit lower-income taxpayers. That undercut efforts in the House against just such a Democratic redistribution of income. It also complicated Reagan's task in a Senate-House tax conference should the Democrats win the House tax fight.

The Republican congressional drift toward parochialism may be inspired by the administration itself. Whereas House Democrats are desperate for victory on the tax bill at any cost, the White House has been silent. The reason: the President and his senior staff admittedly have neglected the most important single Republican legislative proposal since the New Deal to prepare for the Ottawa summit, another in the unending series of forgettable Western diplomatic conferences.

There is other telltale evidence of business as usual within the administration: budgetary retreat under pressure from business interests seeking corporate welfare, including prospective approval of business subsidies for synthetic fuels.

That helps explain why the widely applauded nomination of Judge Sandra O'Connor to the Supreme Court bothered a few thoughtful Republicans (including administration officials) with no overriding interest in the abortion question. They fear this administration may lose its reputation as an instrument of radical change. In that case, Pete Domenici hardly could be criticized for putting Senate prerogatives about the Reagan program.