* House vote to raise debt limit possible Friday
* Senator Cruz ends marathon attack on Obamacare
* Possible government shutdown, default loom in background
WASHINGTON, Sept 25 (Reuters) - The U.S. Congress, already struggling to avert a government shutdown next week, turned its attention on Wednesday to the other fiscal bullet it had to dodge: a federal debt default.
Republican leaders in the House of Representatives notified members that a vote on raising the debt limit could come as early as Friday.
Treasury Secretary Jack Lew pleaded for quick action in the deeply divided Congress on raising the $16.7 trillion statutory limit on government borrowing, as he projected an Oct. 17 date when borrowing capacity would be nearly exhausted and only $30 billion would be left in his agency's checking account.
The non-partisan Congressional Budget Office estimated that after Oct. 22 Treasury might not be able to pay all its bills. The private Bipartisan Policy Center set a range of sometime between Oct. 18 and Nov. 5.
Amid the dire default warnings, lawmakers grappled with another potential crisis: federal agency shutdowns that could begin with the new fiscal year on Oct. 1 unless Congress comes up with emergency funds.
The money would be used to pay U.S. troops, operate border patrols, provide free school lunches for poor children, and for thousands of other activities.
The Democratic-led Senate voted unanimously to begin advancing legislation to avert government agency shutdowns. But both the Senate and the Republican-led House were set for tough fights over the next few days.
Both the debt ceiling and government funding measures were complicated by Republican attempts to use the must-do bills to gut President Barack Obama's signature healthcare law, known as "Obamacare." Democrats are fighting to kill any such efforts.
House Democratic leader Nancy Pelosi of California called for fast passage of a straight-forward debt limit increase, without controversial add-ons.
"Republicans continue to hold the full faith and credit of the United States government hostage to their radical agenda," Pelosi said at a news conference.
Earlier, a disheveled Republican Senator Ted Cruz finished a 21-hour, 19-minute marathon of standing and speaking on the Senate floor, arguing for defunding Obamacare as part of the government-funding bill.
Sporting a beard stubble and his blue tie sagging, the first-term Texas senator with presidential aspirations compared the healthcare law to the villain in the "Friday the 13th" horror films.
"Obamacare is the biggest job-killer in this country and when Jason put on his hockey mask and swung that machete, boy there was carnage like nothing else," Cruz said.
The White House and Democrats in Congress are defending Obamacare, saying it will provide millions of Americans with health insurance that they otherwise could not afford, while potentially pushing down healthcare costs.
With his talk that began at 2:41 p.m. on Tuesday, Cruz approached the 1957 record of 24 hours, 18 minutes, held by late Senator Strom Thurmond, for longest Senate talk marathon.
Senate Majority Leader Harry Reid, a Nevada Democrat, called Cruz's effort "a big waste of time," saying it delayed passage of the legislation to keep the government running.
Representative Steny Hoyer of Maryland, the second-ranking House Democrat, told reporters that the chamber's Republican leaders have not yet reached out to Democrats to discuss keeping the government running and raising the debt limit.
House Democratic votes could end up being crucial to passing either bill if House Speaker John Boehner loses too many of his own Republicans.
Hoyer fretted about the possibility of a government shutdown, saying, "This is the highest risk I have seen because I see the least willingness to do what is absolutely essential in democracy and that is to work together."
House Republicans are likely to huddle early Thursday to try to plan their next moves on the spending and debt limit bills.
SENATE AIMS TO MOVE AHEAD
As the Senate debate on avoiding government shutdowns ground on, leaders there said they hoped for passage by Sunday.
But it was unclear what the House would do with the Senate's product.
Michael Steel, a Boehner spokesman, said: "We'll deal with whatever the Senate passes when they pass it. There's no point in speculating before that."
There have been several trial balloons floated in recent days, including speculation that House Republicans could attach to the Senate bill measures to repeal a medical device tax that collects revenues for operating the healthcare law, a one-year delay in letting individuals sign up for the program and other ideas.
As House Republican leaders plotted out strategy in private, Republican and Democratic senators bickered over the "Affordable Health Care Act," as they have done for nearly five years now.
A New York Times/CBS News poll released on Wednesday underscored Americans have little tolerance for government shutdowns. Eight in 10 people, according to the survey, said it would be unacceptable for Obama or lawmakers to threaten shutdowns during budget negotiations to achieve their goals.
Elected in November 2012, Cruz, a firebrand backed by the conservative Tea Party movement, sometimes strides through the Capitol in cowboy boots. But by Wednesday morning, his feet were clad in tennis shoes that gave him added support as he stood at his lectern or paced the Senate floor for hours. In black, they matched his suit.
"Obamacare isn't working," Cruz said in between stories about his Cuban immigrant father and reciting Doctor Seuss verse.
After Cruz ended his talk marathon, he drew a rebuke from senior Republican Senator John McCain who complained that Cruz had compared those unwilling to embrace his methods to British Prime Minister Neville Chamberlain and others who were willing to appease Nazi Germany before World War Two.
Several Republicans have noted that with Democrats controlling the Senate and White House, there was no way they could prevail in gutting Obamacare.