Democrats on Friday once again postponed a vote on the centerpiece of Joe Biden’s economic vision, after lobbying by the president and House leaders failed to persuade a small group of moderates to support the spending package without delay.

Despite the setback, the House Speaker, Nancy Pelosi, said she planned to plow ahead on the bipartisan infrastructure bill, another key pillar of the president’s legislative agenda, indicating she had the votes to overcome resistance from progressives who want to pass it in tandem with the social policy and climate mitigation spending package.

“We had hoped to be able to bring both bills to the floor today,” Pelosi said at an impromptu news conference on Friday, after a day of frenzied negotiations appeared unlikely to break an impasse over Biden’s agenda.

But Pelosi insisted the House was on the cusp of breakthrough that would not only send the infrastructure bill to Biden’s desk, notching a much-needed victory, but would move the party a “major step” closer to approving the social policy package.

“We’re in the best place ever, today, to be able to go forward,” she said.

A plan to advance both Biden’s social and environmental spending package and a smaller bipartisan public works measure was upended amid pushback from moderates demanding an official accounting of the spending bill.

As tensions escalated, Pelosi proposed a new strategy, announcing in a letter to Democrats that the House would hold two votes on Friday: one on the infrastructure measure and a procedural vote related to the spending package.

But that plan was thrown into jeopardy by progressives, who had for months said they would not vote for the infrastructure bill without a simultaneous vote on the spending package. That position derailed two previous attempts to advance the infrastructure bill first.

The scrambled timeline deflated hopes of giving Biden a much-needed legislative accomplishment after months of false starts and electoral setbacks this week.

Biden and party leaders have worked furiously to reach a consensus on the spending bill, which seeks to combat the climate crisis while reforming healthcare, education and immigration, all paid for by raising taxes on the wealthiest Americans and on corporations. With razor-thin majorities, they need the support of every Democratic senator and nearly every House Democrat.

Centrist lawmakers want to see an independent cost analysis from the non-partisan Congressional Budget Office before voting on the $1.85tn package – which could take several days or even weeks.

In a statement, Washington congresswoman Pramila Jayapal, chair of the Congressional Progressive Caucus, signaled that her members had not softened their position on advancing the bills together.

“If our six colleagues still want to wait for a CBO score, we would agree to give them that time – after which point we can vote on both bills together,” she said.

Negotiations have seen the initial Biden spending proposal nearly halved from $3.5tn, with many provisions pared back or dropped entirely.

Touting a strong monthly jobs report on Friday, Biden implored House Democrats to “vote yes on both these bills right now”, arguing both pieces of legislation were critical to economic recovery.

“Passing these bills will say clearly to the American people, ‘We hear your voices, we’re going to invest in your hopes,” Biden said.

After his remarks, the president said he was returning to the Oval Office to “make some calls” to lawmakers.

Pelosi worked furiously on Thursday to pave the way for a vote before lawmakers leave Washington for a week-long recess, whipping members on the House floor and keeping them late into the night in an effort to shore up support for legislation which runs to more than 2,000 pages.

Democrats suffered a series of stinging electoral setbacks this week, including losing the governorship of Virginia and being run to the wire in New Jersey.

Major legislative victories will, leaders hope, help regain momentum and improve electoral prospects ahead of next year’s midterm elections.

With unified Republican opposition, House Democrats can lose no more than three votes. If passed, the spending bill will go to the 50-50 Senate, where it will face new challenges. Two centrist Democrats, Joe Manchin and Kyrsten Sinema, have already thwarted many proposals and are expected to have further objections.

House passage of the $1.2tn infrastructure bill to upgrade roads, bridges, waterways and broadband, which has already passed the Senate with the support of 19 Republicans, would send the measure to the president’s desk.

The $1.85tn spending package would provide large numbers of Americans with assistance to pay for healthcare, raising children and caring for elderly people at home. There would be lower prescription drug costs and a new hearing aid benefit for older Americans, and the package would provide some $555bn in tax breaks encouraging cleaner energy and electric vehicles, the largest US commitment to tackling climate change.

House Democrats have added other key provisions, including a new paid family leave program and work permits for immigrants.

Much of the cost would be covered with higher taxes on those earning more than $400,000 a year and a 5% surtax on those making more than $10m. Large corporations would face a new 15% minimum tax.

• The Associated Press contributed reporting