WASHINGTON — President Bush vetoed the $300 billion farm bill today, calling it a tax increase on regular Americans at a time of high food prices in the face of a near-certain override by Congress.

It was the 10th veto of Mr. Bush’s presidency. But since it passed both houses of Congress with veto-proof majorities, his action was likely to be canceled out by new votes.

The White House spokeswoman, Dana Perino, said lawmakers should think twice before they do that.

“Members are going to have to think about how they will explain these votes back in their districts at a time when prices are on the rise,” she said. “People are not going to want to see their taxes increase.”

The bill approved earlier this month includes increased subsidies for farmers and food stamps for the poor. With grocery prices going up dramatically, the measure also was sprinkled with pet projects that lawmakers can take home to voters this election year.

Mr. Perino said the bill is $20 billion over the current baseline — “way too much to ask taxpayers right now.”

“This bill is bloated,” she said. “When grocery bills are on the rise, Congress is asking families to pay more in subsidies to wealthy farmers at a time of record farm profits.”