WASHINGTON — The U.S. economy is rebounding from the pandemic downturn faster than expected and is on track to regain all the jobs lost during the coronavirus by the middle of next year, partly as a result of enormous amounts of federal spending that will push the budget deficit to $3 trillion for the 2021 fiscal year, the Congressional Budget Office said on Thursday.

New forecasts that incorporate the $1.9 trillion stimulus package that President Biden signed into law in March give little credence to warnings by Republican lawmakers and some economists that runaway inflation from all that spending could cripple the economy. Instead, the budget office predicted that a recent spike in prices for cars, airline tickets and other products would be temporary and begin to recede this year.

Administration officials downplayed the deficit projections and focused instead on the predictions for economic growth, saying the strong numbers validate Mr. Biden’s push to douse the economy in stimulus and reinforce their view that inflation poses little threat to the recovery.

The budget office, which is nonpartisan, predicted the economy would grow 6.7 percent for the year, after adjusting for inflation. That would be the fastest annual growth in the United States since 1984. It is significantly faster than the budget office and the Biden administration had each projected this year.

The unemployment rate is also estimated to fall below 4 percent next year and remain historically low for years to come, signaling a significant acceleration in job gains from what the office predicted in February. The C.B.O. said then that unemployment would not fall below 4 percent until 2026.

Budget office officials said the uptick in growth and employment forecasts stemmed in large part from aggressive government stimulus. But the economy is also benefiting from consumers, who are rapidly spending savings they built up during the pandemic. Households were buttressed by multiple rounds of stimulus, including direct checks, passed under President Donald J. Trump, and by a faster-than-anticipated return to normalcy in the economy as vaccinations have spread.

Mr. Biden’s aides claimed credit for many of those developments. They said the president’s push to accelerate vaccine production and distribution had fueled the reopening of the economy. David Kamin, a deputy director of the White House National Economic Council, said in an interview that Mr. Biden’s stimulus package, the American Rescue Plan, was intended to drive a more rapid return to low unemployment, and that the budget office’s projections were evidence it was succeeding.

“This report really goes to the very theory of the case as to why we pursued a rescue plan,” he said.

Administration officials also heralded updated projections from the International Monetary Fund, released Thursday afternoon, which predicted the U.S. economy would grow 7 percent in 2021 after adjusting for inflation. In April, the I.M.F. forecast 4.6 percent growth for the year in the United States.

Mr. Biden’s stimulus plan will push the federal budget deficit near record highs for the fiscal year, the budget office projected, but it will eventually leave the country in slightly better fiscal shape.

The spending approved by Mr. Biden is projected to increase the deficit by $1.1 trillion for the fiscal year, which ends in September. The total deficit of $3 trillion would be the second-largest since 1945, in nominal terms and as a share of the economy, behind the 2020 fiscal year.

But the increased growth that is accompanying the larger deficit this year will slightly improve the country’s fiscal outlook over the next decade, with the total deficit falling by about 1 percent, the budget office said.

“Projected revenues over the next decade are now higher because of the stronger economy and consequent higher taxable incomes,” it wrote in its report.

Mr. Biden’s rescue plan included direct payments of $1,400 each to low- and middle-income Americans, $350 billion to help states and municipalities patch what were expected to be budget shortfalls and hundreds of billions of dollars to accelerate vaccines and more widespread coronavirus testing. It also extended supplemental federal payments of $300 a week to unemployed workers through September, a benefit that Republican governors across the country have ended early as business owners complain of difficulties finding workers.

The budget office cited those benefits as “dampening the supply of labor,” along with workers’ health concerns. It said the expiration of the benefits, along with less worry about contracting the virus, would help bolster employment growth in the second half of this year.

Inflation, which has been a big topic in Washington, is projected to moderate in the months to come. The office forecast inflation rising above recent trends to hit 2.6 percent for the year, which is stronger growth than the February projection, yet officials see those price pressures subsiding in the second half of the year, as a variety of supply constraints ease in areas like lumber and automobiles.

The forecasters expect economic growth to continue at a strong pace in 2022, hitting 5 percent in real terms. But they see it declining quickly in the years to follow, as the labor force grows more slowly than is typical. Budget office officials said that reflected, in part, the effects of more restrictive immigration policies adopted under Mr. Trump. By 2023, the office predicts, growth will slow to 1.1 percent.

That forecast does not account for any additional economic policies Mr. Biden might enact in the intervening time. He is currently pushing Congress to approve as much as $4 trillion in spending and tax cuts meant to create jobs and aid growth by improving the productivity of workers and the broader economy, like repairing bridges and subsidizing child care costs to help more parents, particularly women, work additional hours.

Fiscal hawks said the report’s long-term deficit projections underscored the need for any additional economic investments to be fully paid for, and not financed with federal borrowing. Debt held by the public rises to nearly $36 trillion by 2031, the budget office now predicts. That would be slightly larger — by just over 6 percent — than the size of the total American economy that year.

“While it made sense to borrow to weather the pandemic and jumpstart the recovery,” said Maya MacGuineas, the president of the Committee for a Responsible Federal Budget in Washington, “the strong economic growth projections from C.B.O. show that it is time to pivot away from further deficit-financing and towards paying for things and, ultimately, decreasing the national debt from its current path.”