(Adds canceled Senate recess, progress in negotiations, Senator Cassidy)
WASHINGTON, March 12 (Reuters) - The U.S. Congress on Thursday struggled to pass legislation to deal with the expanding coronavirus crisis, as House of Representatives Speaker Nancy Pelosi haggled by telephone with Treasury Secretary Steven Mnuchin to try to agree a deal.
Earlier, Republicans had called the Democratic bill "unworkable." By mid-afternoon, several Democrats had emerged from Pelosi's office saying they thought progress was being made.
The Democrats' 124-page "Families First Coronavirus Response Act" will be debated on the House floor on Thursday, Pelosi said in a morning press conference.
She also said she was negotiating with the Trump administration over provisions such as paying for a free coronavirus testing program.
The Democrats' bill would expand paid sick leave, unemployment insurance, funding for child nutrition, and other food programs, and introduce other sweeping steps to address economic hardships that the outbreak could wreak on Americans.
But Republicans expressed doubts. Senator Majority Leader Mitch McConnell kicked off Thursday's Senate session by saying the bill was "an ideological wish list" that would create new, burdensome programs and regulations. Republicans have particularly voiced concerns over the extent of a paid leave program.
McConnell urged bipartisan efforts at passing "smaller, non-controversial pieces of legislation today," without elaborating.
Last week, Congress displayed unusual bipartisanship when it passed an $8.3 billion coronavirus response bill that attracted only a few 'no' votes. But this week, the poisonous partisan atmosphere was back, as the U.S. government wrestled with responding to the biggest health crisis it has faced in years.
House Democrats emerged from a closed meeting noting progress in negotiations with the White House. "We are closing in on the target," said Representative Jamie Raskin.
Pelosi aide Drew Hammill said she had held four telephone calls with Mnuchin so far on Thursday, but did not provide details.
House Minority Leader Kevin McCarthy, a Republican, said Pelosi's bill was "not only completely partisan. It is unworkable." He suggested a bipartisan plan could be worked out within 48 hours.
But Pelosi said Congress needed to address an emergency facing the country and suggested that some Republican concerns could be addressed in subsequent legislation.
"We don't need 48 hours. We need to just make a decision to help families right now," Pelosi told reporters.
Democrats and some Republicans in Congress have been frustrated that the United States was ill-prepared to conduct widespread testing for the coronavirus.
That was underscored early on Thursday when senators emerged from a closed briefing with top U.S. health officials.
Democratic Senator Richard Blumenthal told reporters the attending physician of Congress, Dr Brian Monahan, estimated 70 million to 150 million people would contract the coronavirus in the United States.
Blumenthal said he thought the estimates were guesswork because of "insufficient testing" for the disease so far.
Republican Senator Mike Rounds said the health officials were having trouble giving them details on how many test kits were needed and "there was lots of frustration that we were not getting the numbers we were hoping to get."
Several senators also said there was an issue with the supply chain for items needed to administer the tests, such as cotton swabs and protective gloves.
Meanwhile, a crisis atmosphere enveloped the Capitol, where tourist visits were suspended at least until April 1 and at least two Senate offices were shuttered over worries about possible infections.
At a Senate Republican lunch, Senator Bill Cassidy, a medical doctor, told reporters he argued for allowing senators to cast votes on legislation remotely in emergency situations, an idea congressional leaders have been resisting.
The urgency to act has been heightened by Congress' work schedule.
The House was aiming to start a recess at the end of the week, but the Senate intends to work next week on coronavirus legislation that would be different from a House version.
New legislation would be the second in two weeks, following last week's enactment of the $8.3 billion bill to help develop a coronavirus vaccine and finance steps to contain and treat the potentially fatal disease that the virus can cause.
McCarthy complained it could take the Social Security Administration more than six months to get a paid sick leave program in the bill operating.
(Reporting by Susan Cornwell, David Morgan, Richard Cowan and Lisa Lambert; Writing by Richard Cowan; Editing by Bernadette Baum and Rosalba O'Brien)