The nation's unemployment rate shot up abruptly from 6.2 to 7 percent of the work force in April, the largest one-month increase since early in the 1974-75 recession, the government reported yesterday.

The swiftness of the increase has many economists fretting that the current recession may prove substantially more severe than earlier expected.

The increase was pervasive, with especially heavy layoffs among blue-collar workers, particularly in the hardhit auto and housing sectors. The number of Americans out of work soared by 827,000 to 7.3 million. The number of jobs in the economy shrank by 502,000.

The darkening of the job picture brought criticism of the White House and Federal Reserve Board and speculation that the administration soon would propose a tax cut to stimulate the economy. Until now, it has been moving in the opposite direction, working to balance the budget to fight inflation.

Immediately after the jobless figures were made public, AFL-CIO President Lane Kirkland visited the White House for talks with Vice President Mondale and Carter economic advisers. Aides said no decisions were made.

Kirkland later issued a statement calling on the president and Congress to abandon current budget-cutting plans and vote new job programs. He called the administration's present economic policies "misguided."

Treasury Secretary G. William Miller sought to downplay the significance of the sharp increase in the unemployment rate, saying it was "substantial" but "it would not be prudent to read too much into a single month's statistics."

"It is especially important not to allow monthly statistics to divert us from our longterm economic object -- which is to return the economy to stable growth at a significantly reduced rate of inflation," Miller said.

In Memphis, Republican presidential front-runner Ronald Reagan cited the new figures on joblessness as evidence of the administration's "ineptitude" in handling the economy. Reagan said Carter "got us into the mess we're in."

However, both White House and congressional leaders said they have no intention of altering course, at least for the foreseeable future, and will hold to present budget-balancing plans.

Outside analysts, however, noted that if the recession proves deeper than Carter has forecast, it will be impossible to balance the budget because of higher outlays for unemployment benefits, food stamps and other welfare payments.

The April increase in the jobless rate was the sharpest for any one month since January 1975, near the start of the 1974-75 recession. The unemloyment rate has not been this high since August 1977.

As was widely anticipated, the increase in joblessness hit hardest in the auto and construction industries. The unemployment rate among auto workers stood at 21.5 percent in April. The rate for construction workers was 15.1 percent.

But the losses spread pervasively into retail trade and other major sectors of the economy as well. The jobless rate among adult men surged a full percentage point, to 5.9 percent. The rate among factory workers jumped to 7.9 percent.

The only major group to escape a serious increase was teen-agers, whose jobless rate edged up only 0.3 percent. Joblessness among black youths actually fell, to 29.8 percent, from 33 percent before.

The decline in overall employment levels brought the total job loss over the past two months to a sizable 800,000 slots. In the first four months of this year, the job loss has been 1.2 million.

The Labor Department's survey showed that industry payrolls shrank by 479,000 in April, the largest monthly reduction since December 1974. Factory overtime also dropped 0.3 hours, and the length of the work-week edged down.

The increase in April marked the first major change in the unemployment rate in almost two years. For the previous 20 months, the jobless rate had hovered in the 5.8-to-6 percent range economists consider to be "full employment."

The White House and the Federal Reserve Board have been trying to brake the economy in hopes of easing inflation pressures. Carter's March 14 anti-inflation package was designed to bring on a recession Carter said would be "mild and short."

However, yesterday, Alan Greenspan, former president Ford's chief economic adviser, said his own calculations now call for a deep decline in output in the current quarter that is difficult "to square with any forecasts of short and mild."

And House Banking Committee Chairman Henry S. Reuss (D-Wis.) warned that the "startling" rise in the unemployment rate should alert the Fed to the danger of "overstaying" its current money and credit restrictions.

The new figures yesterday also gave rise to renewed calls by conservatives for a new set of business tax breaks to spur productivity. Sen. Lloyd M. Bentsen (D-Tex.), chairman of the congressional Joint Economic Committee, urged such a move.

Meanwhile, the Ford Motor Co. announced that it will temporarily lay off about 2,300 workers at its suburban Cleveland plant as a result of the continued slump in auto sales. Auto layoffs now total 265,000.

As usual, the increase in joblessness did not hit all sections of the nation evenly. In Michigan, Ohio and California, unemployment rose sharply, topping 12.2 percent in Michigan and 7.4 percent in Ohio.

However, the jobless rate in Texas declined during April, to 5.4 percent, from 5.8 percent in March, and the unemployment rate in New York city plunged to 7.5 percent, from 8.8 percent before.

In a related development yesterday, President Carter sent Congress a request for a $1.5 billion supplemental appropriation to provide unemployment compensation of auto workers who have been laid off because of foreign imports. c

The additional compensation to auto workers is authorized by the Trade Adjustment Assistant Act. Carter requested $1.1 billion for the current fiscal year and $400 million for the fiscal year that begins Oct. 1.