The Senate approved a $450 billion extension of the federal debt limit Tuesday and threw the matter back to the House, where election-year politics has prevented a direct vote.

The Democratic-controlled Senate approved the increase by 68-29 after Republicans decided against offering major amendments. Boosting the current $5.95 trillion debt ceiling by $450 billion is expected to provide enough room for the government to borrow money until at least December -- after the November elections for control of the House and Senate.

The Bush administration has said the limit must be increased by June 28 or the government will face default for the first time in history. The last time the debt ceiling was raised was in 1997, just before annual federal deficits turned into surpluses.

A federal default is considered unthinkable because it would irrevocably harm the government's credit rating, adversely affecting interest rates and the world economy. Because of that, Congress' legal obligation to periodically increase the borrowing limit has invariably become a political battlefield.

Senate Democrats have favored addressing the issue because they feel they must as the chamber's majority. Republicans considered offering amendments that would clamp controls over federal spending, but opted not to after realizing they lacked the votes to prevail and might be seen as delaying the legislation.

In the GOP-led House, Republican leaders have not held a separate debt limit vote because they lack the support to pass it.

Many Republicans, especially conservatives, are reluctant to vote for more federal borrowing. House Democrats overwhelmingly oppose an extension to beyond the elections because they blame President Bush's tax cut of last year for the renewed need to seek additional borrowing, and want to spend time publicizing the issue.

Instead, GOP leaders included a provision in the $29 billion anti-terrorism bill the House approved last month that would let the issue come up in House-Senate bargaining over a final version of the anti-terror bill.

Administration officials initially sought a debt limit increase in December. When the government approached its borrowing cap earlier this spring, Treasury Secretary Paul O'Neill dipped into federal accounts his agency controls to keep the government from breaching the borrowing ceiling, a legal maneuver.