Mayor Bloomberg is letting the public into his thought process more and more as he weighs a run for the White House. A Connecticut newspaper, the Hour, reported that over the weekend Mr. Bloomberg said he thought he could have more influence as a private philanthropist than as the American president.

Whether to launch a project as all-consuming as a presidential bid involves a complicated calculus for any politician. And doubtless Mr. Bloomberg would be as effective a philanthropist as he has been a mayor, which is saying quite a bit. This column is a champion of the private sector and of private philanthropy. Even so, it’s hard to credit Mr. Bloomberg’s analysis on the influence front. The great presidents – Lincoln, Roosevelt, Reagan – are far more famous than the great philanthropists such as Andrew Carnegie.

Forbes magazine, which regularly includes the mayor on its list of richest individuals, estimates his net worth at $5 billion. It’s a significant sum by any reckoning, except, that is, in comparison to the federal budget. For fiscal 2007, President Bush has submitted a budget request that envisions spending $2.77 trillion, and forecasts that government spending will rise to $3.06 trillion by fiscal 2010, the first budget a President Bloomberg would propose. The federal government will spend an amount equal to Mr. Bloomberg’s entire fortune every 15 hours and 49 minutes.

Mr. Bloomberg’s much-heralded $30 million gift to the Carnegie Corporation of New York? Washington is set to spend that amount every five minutes and 42 seconds. Even if Mr. Bloomberg is worth three times what Forbes says he is worth, the mayor’s entire fortune would amount to about two days worth of federal spending.

A president doesn’t have sole spending authority; there is Congress to reckon with. But Mr. Bloomberg has experience in that regard with the City Council, which he has dominated. And influence involves not only spending power but also executive orders and policy direction; imagine if the mayor’s speech in Atlanta Wednesday hadn’t been only in the nature of a call for action but had actually been an instruction to a Centers for Disease Control and Prevention that Mr. Bloomberg actually had authority over as part of the executive branch.

There would still be plenty of time for Mr. Bloomberg to dispose of his personal wealth after his four or eight years in the Oval Office wrap up, or after he had enriched the American political debate by chancing a hard-fought though ultimately losing presidential campaign. There may be reasons for Mr. Bloomberg not to do it. But the idea that he could do more good or have more influence as a private philanthropist is not a strong reason not to run.