WASHINGTON  In leading his colleagues in a vote on Tuesday to ban the lawmaker-directed spending items known as earmarks, Mitch McConnell, the Senate Republican leader and consummate Congressional appropriator, averted a divisive clash within his caucus over the question of joining the new House Republican majority in enacting an earmark “moratorium” for the next Congress.

Given how zealously Mr. McConnell has defended the constitutional prerogative of Congress to control the federal purse, his turnabout was also the surest sign yet that the rightward pressure of Tea Party groups, and an antispending sentiment among voters, have begun to influence the way Washington does business.

At the same time, the renewed push against earmarks highlighted a potential conflict between the calls to eliminate the spending items and demands by many Tea Party supporters for greater fidelity to the Constitution. It is the Constitution, after all, that put Congress in charge of deciding how to spend the taxpayers’ money. In pledging not to let individual lawmakers designate federal money for local purposes, the anti-earmark contingent is in effect ceding more power to the executive branch over how taxpayer dollars are spent, presumably not the outcome desired by the new crop of grass-roots conservatives.

“If Congress does not direct any spending,” said Senator Kay Bailey Hutchison, Republican of Texas, who supported the earmark ban, “the president will have 100 percent of the discretion in all federal programs. The failed stimulus is replete with examples of the president’s earmarks that are wasteful.”