The nation's unemployment rate soared to a post-World War II record of 9.4 percent last month, with 10.3 million Americans out of work, the government reported yesterday.

Black unemployment climbed to a postwar peak of 18.4 percent in April, the Labor Department said, and the jobless rates for adult men, teen-agers and blue-collar workers all hit their highest levels since the Great Depression.

In a further sign of the depressed state of the labor market, the number of jobs dropped last month by 152,000, bringing the total job loss since the recession began last July to 1.5 million, the department said.

Many economists warn that unemployment may rise still higher in coming months, even if the recession ends soon. The Business Council, a group of 200 top businessmen, said yesterday that while their members believe the recession is now ending they expect only a weak recovery this year.

White House deputy press secretary Larry Speakes would not predict when the employment picture might start to improve, but told reporters, "We're looking for signs of economic recovery by late spring-early summer."

The administration originally predicted that a strong recovery would begin this spring, and many analysts had expected the recession might touch bottom in March or April.

However, yesterday's job figures made it "clear that the economy was sinking rapidly in April," analyst Donald Straszheim of Wharton Econometrics said. He predicted that figures published next week will show a "striking decline" in the nation's industrial output for April.

Persistently high interest rates have prolonged the recession, analysts say. The Federal Reserve yesterday reported a big drop of $4.9 billion in the money supply in the last week of April, which some experts said could pave the way for a slight easing of money and thus of rates next week. However, others believe that the money markets will remain tight in the next few days.

Last month's jobless rate was the highest since the 9.9 percent recorded for 1941, at the end of the Depression. It represented a rise of 0.4 percent from the March level, which at 9 percent had equalled the previous postwar peak of May, 1975.

There was a seasonally adjusted rise of 453,000 in the number of unemployed last month, yesterday's report said. Since the recession began last summer the number out of work has climbed by 2.5 million, Janet Norwood, commissioner of the Bureau of Labor Statistics, said. The jobless rate has risen from 7.2 percent in July, 1981, to 9.4 percent.

In addition to those thrown out of work by recession, 5.8 million people were forced to work part-time in April because they could not find full-time jobs. This, too, was a record, the highest since the Labor Department began to collect these numbers in 1955. It was a rise of 117,000 from March, and 1.5 million from last July.

Cutbacks in construction and factory jobs were particularly marked last month. The jobless rate for blue-collar workers shot up to 13.7 percent from 12.9 percent in March. White-collar unemployment edged up to 4.9 percent from 4.8 percent in March.

Industrial jobs declined by 200,000 in April, after seasonal adjustment, with most of the fall accounted for by sharp declines of 85,000 and 80,000 respectively in construction and manufacturing. In the last year nearly one in 10 construction jobs has been lost, the Labor Department said.

"Employment in manufacturing industry is especially sensitive to recession," Norwood said, pointing out that for several manufacturing industries "the number of payroll employes in April was below the level reached at the trough of the 1975 recession." Even in retail trade, a "traditional growth industry," jobs have risen less than 100,000 since last July, and fell by 70,000 in April after seasonal adjustment.

The rise in unemployment affected most groups in the economy, Norwood said. The jobless rate for adult men rose from 7.9 percent in March to a postwar record of 8.2 percent; that for adult women went from 7.9 percent to 8.3 percent; and for teen-agers it rose from 21.9 percent to 23 percent.

Employment and unemployment are heavily influenced by seasonal trends, and the BLS adjusts the raw data to take account of these when it measures the underlying job market. President Reagan last month used the raw, unadjusted figures to tell school children that unemployment had actually fallen in March, rather than had risen, as generally reported.

Norwood was careful yesterday to note that the unadjusted jobless figure fell again in April, but since the drop was much less than usual for that time of year the adjusted figures showed a sharp rise in unemployment. Those are the numbers analysts use to judge what is happening.