WASHINGTON, Oct 4 (Reuters) - President Joe Biden said on Monday the federal government could breach its $28.4 trillion debt limit in a historic default unless Republicans join Democrats in voting to raise it in the two next weeks. Senate Republicans, led by Minority Leader Mitch McConnell, have twice in recent weeks blocked action to raise the debt ceiling - saying they do want action but will not help. Republicans say Democrats can use a parliamentary maneuver known as budget reconciliation to act alone. Top Democrats have rejected that approach. "Raising the debt limit comes down to paying what we already owe ... not anything new," Biden said at a White House news conference. Asked if he could guarantee the United States won"t breach the debt limit, the president answered: "No I can"t. That"s up to Mitch McConnell." He said he intended to speak with McConnell about the matter.McConnell for months has been saying that Democrats should use budget reconciliation to get around the Senate"s filibuster rule, which requires 60 of 100 members to agree to pass most legislation. Senate Majority Leader Chuck Schumer, a Democrat, has refused that approach and Biden on Monday pleaded for Republicans not to use the filibuster to block action. "Just get out of the way," Biden told Republicans. "If you don"t want to help save the country, get out of the way so you don"t destroy it." But Senator Joe Manchin, a moderate Democrat who has been at odds with many in his party on other major issues, said Democratic leaders should not rule out using budget reconciliation to raise the debt ceiling. "Well they shouldn’t rule out anything - we just can’t let the debt ceiling lapse," Manchin said, according to CNN reporter Manu Raju, who tweeted the senator"s comments. Late last month the U.S. House of Representatives passed and sent to the Senate a bill to suspend the limit on Treasury borrowing through the end of 2022. Schumer on Monday said that later this week the Senate would vote on a measure to suspend the debt limit, the third time he has sought to bring it up. Treasury Secretary Janet Yellen last week warned lawmakers that the United States government was close to exhausting its federal borrowing capabilities by about Oct. 18. Failure to act could have catastrophic economic consequences. Moody"s last month warned that it could cause a nearly 4% decline in economic activity, the loss of almost 6 million jobs, an unemployment rate of close to 9%, a sell-off in stocks that could wipe out $15 trillion in household wealth and a spike in interest rates on mortgages, consumer loans and business debts. Democrats voted to raise the debt limit during Republican Donald Trump"s administration even though they opposed deep tax cuts that added to the debt. Biden said the United States racked up nearly $8 trillion in new debt over Trump"s four years in office, more than one quarter of the entire debt outstanding. "Republicans in Congress raised the debt three times" under Trump, he said, with Democratic support. STOCKS SLIDE Concerns over the debt ceiling contributed to Monday"s drop in the stock market. Wall Street"s main indexes tumbled on Monday as investors shifted out of technology stocks in the face of rising Treasury yields, with concerns about U.S.-China trade, Taiwan and the debt ceiling in the forefront. McConnell stuck to his guns on Monday. "The majority needs to stop sleepwalking toward yet another preventable crisis. Democrats need to tackle the debt limit," McConnell said on the Senate floor. In an open letter to Biden, McConnell said that the Democrats do not need Republican cooperation to pass a bill to raise the debt ceiling. Democrats have had nearly three months notice from Republicans about their position on the matter, McConnell wrote. McConnell is known for standing his ground once he takes a controversial position. For example, in 2016 he refused to allow a Senate hearing on then-President Barack Obama"s nomination of Merrick Garland to a seat on the Supreme Court - holding the seat open until after Trump assumed office nearly a year later. Schumer said the Senate will have to stay in session through the weekend and possibly into a planned recess next week if no progress is made on raising the debt limit. Last week, the Senate"s parliamentarian ruled that Schumer could use the budget reconciliation process to bring a debt limit bill to the Senate floor, according to a source familiar with the ruling. According to the parliamentarian, doing so would not jeopardize Democrats" efforts to bring a second bill to the Senate floor under reconciliation. That is the multitrillion-dollar bill embracing Biden"s domestic agenda expanding social services and addressing climate change that Democrats are developing. Reporting by Susan Cornwell, Richard Cowan and Jarrett Renshaw; additional reporting by David Morgan, Jeff Mason, Steve Holland, Diane Bartz and Eric Beech; Editing by Scott Malone, Mark Porter and Grant McCool Our Standards: The Thomson Reuters Trust Principles.