WASHINGTON -- In the 1920s and '30s, the American left was driven by multiple factions furiously representing different flavors of socialism, each accusing the others of revisionism and deviationism. Leftists comforted themselves with the thought that "you can't split rotten wood."

But you can. And the health of a political persuasion can be inversely proportional to the amount of time its adherents spend expelling heretics from the one true (and steadily smaller) church. Today's arguments about conservatism are, however, evidence of healthy introspection.

The most recent reformer to nail his purifying theses to the door of conservatism's cathedral is Michael Gerson, a former speechwriter for the current president, and now a syndicated columnist. He advocates "Heroic Conservatism" in a new book with that trumpet-blast of a title.

His task of vivifying his concept by concrete examples is simplified by the fact that he thinks the Bush administration has been heroically conservative while expanding the welfare state and trying to export democracy. His task of making such conservatism attractive is complicated by the fact that ... well, it is not just the 22nd Amendment that is preventing the president from seeking a third term.

Gerson, an evangelical Christian, makes "compassion" the defining attribute of political heroism. But compassion is a personal feeling, not a public agenda. To act compassionately is to act to prevent or ameliorate pain and distress. But if there is, as Gerson suggests, a categorical imperative to do so, two things follow. First, politics is reduced to right-mindedness -- to having good intentions arising from noble sentiments -- and has an attenuated connection with results. Second, limited government must be considered uncompassionate, because the ways to prevent or reduce stress are unlimited.

"We have a responsibility," Bush said on Labor Day 2003, "that when somebody hurts, government has got to move." That is less a compassionate thought than a flaunting of sentiment to avoid thinking about government's limited capacities and unlimited confidence.

Conservatism is a political philosophy concerned with collective aspirations and actions. But conservatism teaches that benevolent government is not always a benefactor. Conservatism's task is to distinguish between what government can and cannot do, and between what it can do but should not.

Gerson's call for "idealism" is not an informative exhortation: Huey Long and Calvin Coolidge both had ideals. Gerson's "heroic conservatism" is, however, a variant of what has been called "national greatness conservatism." The very name suggests that America will be great if it undertakes this or that great exertion abroad. This grates on conservatives who think America is great, not least because it rarely and usually reluctantly conscripts people into vast collective undertakings.

Most Republican presidential candidates express admiration for Theodore Roosevelt. A real national greatness guy ("I have been hoping and working ardently to bring about our interference in Cuba"), he lamented that America lacked "the stomach for empire."

He pioneered the practice of governing aggressively by executive orders. Jim Powell, author of "Bully Boy," an unenthralled assessment of TR, says that in the 40 years from Abraham Lincoln through TR's predecessor, William McKinley, presidents issued 158 executive orders. In seven years, TR issued 1,007. Only two presidents have issued more -- TR's nemesis Woodrow Wilson (1,791) and TR's cousin Franklin Roosevelt (3,723).

"I don't think," TR said, "that any harm comes from the concentration of power in one man's hands." That sort of executive swagger is precisely what Washington does not need more of. It needs more conservatives such as David Keene, chairman of the American Conservative Union for 23 years and Southern political director of Ronald Reagan's 1976 presidential campaign. Writing on "The Conservative Continuum" in the September/October issue of The National Interest, Keene says of Reagan:

"He resorted to military force far less often than many of those who came before him or who have since occupied the Oval Office. ... After the (1983) assault on the Marine barracks in Lebanon, it was questioning the wisdom of U.S. involvement that led Reagan to withdraw our troops rather than dig in. He found no good strategic reason to give our regional enemies inviting U.S. targets. Can one imagine one of today's neoconservative absolutists backing away from any fight anywhere?"

It is a pity that TR built the Panama Canal. If he had not, "national greatness" and "heroic" conservatives could invest their overflowing energies and vaulting ambitions into building it, and other conservatives -- call them mere realists -- could continue seeking limited government, grounded in cognizance of government's limited competences. That is an idealism consonant with the nation's actual greatness.