WASHINGTON — In a resounding break from President Bush, a majority of Senate Republicans joined Democrats yesterday in approving a war-funding bill that would provide for a major new expansion of the World War II-era GI Bill.

The measure must be approved by the House, and it faces a threatened White House veto. But the Republican defections — followed by a lopsided vote to override Mr. Bush’s veto of a farm bill — underscored a growing willingness among Republicans to go their own way as they look ahead.

The new veterans’ education benefit also erupted as an issue in the presidential campaign, as the Democratic presidential candidate, Senator Obama of Illinois, and the presumptive Republican presidential nominee, Senator McCain of Arizona, exchanged sharp words.

The White House has objected to the billions of dollars in spending included for such things as jobless benefits, energy assistance, and brush clearance, which brought the bill’s total to about $212 billion, including $165 billion for the wars in Iraq and Afghanistan.

“This is the wrong way to consider domestic spending, and Congress should not go down this path,” the White House spokeswoman, Dana Perino, said.

The Pentagon has expressed concern that the new GI benefit, while providing returning troops a free college education after three years of active duty, could spur retirements at a time the military is struggling to retain soldiers.

But lawmakers were eager to show support for the troops before Memorial Day.

Mr. Obama and his rival for the Democratic presidential nomination, Senator Clinton, broke off campaigning to return to the Capitol to vote for the GI benefit.

Mr. Obama, taking a shot at Mr. McCain, said, “I respect Senator John McCain’s service to our country. … But I can’t understand why he would line up behind the president in opposition to this GI bill.”

Mr. McCain was attending campaign events in California during the vote, but responded in a lengthy statement that Mr. Obama has “less than zero understanding” of the issue.

“It is typical, but no less offensive, that Senator Obama uses the Senate floor to take cheap shots at an opponent,” Mr. McCain said. “And I will not accept from Senator Obama, who did not feel it was his responsibility to serve our country in uniform, any lectures on my regard for those who did.”