Democratic leaders announced the US House would vote Friday on President Joe Biden's $3 trillion blueprint to transform transport networks and expand the welfare safety net.

House Democratic leaders had been hoping for a procedural vote on Biden's $1.75 trillion Build Back Better social spending plan and to rubber-stamp the Senate-passed $1.2 trillion infrastructure package on Thursday but outstanding differences among lawmakers on the details forced a delay.

"This Build Back Better agenda, along with the bipartisan infrastructure bill, as we have said, is transformational, and it's historic, and it's important to get this done," White House spokeswoman Karine Jean-Pierre told reporters.

"And so the president is going to continue to work with members in Congress to make that happen."

A green light from the House on infrastructure would pave the way for a history-making upgrade of the country's crumbling roads, bridges, waterways and broadband network.

The social spending package doesn't have Senate blessing, however, and is some way from becoming law.

The lower chamber going full-speed ahead on the larger bill after months of delays caused by infighting is largely a pressure tactic to light a fire under senators in hopes a House-passed bill spurs them into action in the coming month.

That push leaves House lawmakers facing the prospect of having the bill sent back to them from the upper chamber with significant changes, while the infrastructure legislation merely needs majority support in the House to advance to Biden's desk.

'Too far left'

House Speaker Nancy Pelosi told reporters earlier in the day she was "very unhappy" to have failed twice in recent weeks to pass the infrastructure bill and was determined that both bills could move together quickly.

The events on Capitol Hill were being closely watched by the president, who spent the evening telephoning members to ask for yes votes on both bills, congressional media outlets reported.

Biden returned from an overseas trip Wednesday to a party floored by a Republican sweep in Virginia elections and razor-thin victory instead of the expected landslide in the race for governor of New Jersey.

The Democrats are desperate to avoid repeating those kinds of setbacks in next year's midterm elections, although many observers are unconvinced that the coming bloodbath can be averted by any action in Congress.

House minority leader Kevin McCarthy has predicted Republicans, who have 213 representatives compared with the Democrats' 221, could flip more than 60 House seats next year, repeating the Tea Party wave of 2010.

Either way, Tuesday's poor returns leave Democrats with a dilemma: Is Biden's agenda too progressive for the political center, or is it so diluted from its ambitious prototype that it won't enthuse the left?

The answers offered by the various factions tend to match their established political positions, with conservatives calling for a handbrake on the social spending and liberals redoubling efforts to get both bills passed.

Senate holdout Joe Manchin is influenced by the University of Pennsylvania's Wharton School, which assesses that the $1.75 trillion Build Back Better price tag would increase to almost $4 trillion if its provisions become permanent.

"We can't go too far left. This is not a center left or a left country," the conservative West Virginia Democrat, who has made clear he will not be swayed by whatever the House passes, told CNN on Thursday.

'Pouring gasoline on inflation'

In reality, Build Back Better polls extremely well across America, which has only handed a Republican president the popular vote once since the 1980s.

A Thursday report from Moody's concludes the two bills would add 1.5 million jobs a year and grow the economy by nearly $3 trillion over the next decade.

Echoing Manchin's prudence, five House moderates had insisted on a budgetary score to ensure that the bill is "fiscally responsible" before they will vote, which would likely take two weeks.

Perhaps the biggest sticking point though is immigration, with three Latino lawmakers opposed to any version of Build Back Better that doesn't provide a pathway to citizenship for undocumented immigrants.

But Pelosi prides herself on never bringing votes to the floor that she doesn't already know have enough support to pass -- suggesting that rank-and-file lawmakers had been placated.

The Republicans have largely made themselves irrelevant in the negotiations by ruling out support for any social spending bill from day one, instead enjoying the Democratic circular firing squad from the sidelines.

But Lindsey Graham, the senior Republican on the Senate budget committee, gathered reporters Thursday to offer his characterization of Build Back Better as a "fraud that's going to be pouring gasoline on inflation."