Unemployment climbed to 9 percent last month, matching the previous post-World War II peak of May 1975 and leaving nearly 10 million Americans out of work, the Labor Department reported yesterday.

Black unemployment jumped from 17.3 percent to 18 percent in March, more than twice the rate for whites, the government said.

Reagan administration officials accept that unemployment is likely to rise still higher in coming months, although they predict that economic recovery later in the year will reverse the trend. Several private analysts are less optimistic and say there is no sign yet of a recovery that will reduce unemployment.

While the White House called the March unemployment figures "disappointing" and said that "the president feels this keenly," Democrats and labor leaders seized on the news as evidence that President Reagan's policies are not working.

"More families are more desperate now with less hope for the future than at any time since the Great Depression," Sen. Edward M. Kennedy (D-Mass.) said. "America's unemployed workers don't want more promises, they need jobs now," said AFL-CIO economist Rudy Oswald, adding that Reagan's "budget, tax and monetary policies are making the situation worse."

Layoffs added 280,000 to the jobless total in March, pushing it to 9.9 million, the Labor Department said. This is 2 million above the low point last July before the recession began, and 1.8 million higher than the jobless total when Reagan took office. The official unemployment tally nevertheless understates the number of Americans affected by the current poor job market. Last month, a record 5.7 million people were forced by "economic conditions" to work shorter hours than they wanted to, a rise of 150,000 from February and 1.7 million from the 1981 low last June, the Labor Department said.

In addition, there were a record 1.3 million people in the first three months of this year who wanted to work but were too "discouraged" to look for jobs and so did not count as officially unemployed, the Labor Department said. This represents a rise of 140,000 from the final quarter of 1981, and 300,000 since the recession began.

Blacks have been disproportionately hit by the recession and loss of job opportunities, Bureau of Labor Statistics Commissioner Janet L. Norwood told a congressional panel yesterday. She said that "blacks comprise 10 percent of the population, but they constitute 20 percent of the unemployed and nearly 40 percent of the discouraged." Oswald commented that "it is worse than a recession . . . it is a depression for black Americans."

Critics have charged that Reagan's policies hit the poor and minorities harder than others. The president called this "a fairy tale" in his news conference on Wednesday. He has also criticized the news media for concentrating on the bad economic news, such as high interest rates and unemployment, rather than the good news about inflation. White House communications director David R. Gergen repeated this theme yesterday.

The overall unemployment rate for March was 0.2 of a percentage point higher than in February and 1.8 percentage points up from the low point last July, yesterday's Labor Department report said. About 60 percent of the rise in unemployment has been among adult males, Norwood told the Joint Economic Committee of Congress.

Unemployment among adult men and adult women rose from 7.6 percent to 7.9 percent last month. For men this matches the previous post-World War II peak of last December, when national unemployment hit 8.9 percent. However, the previous postwar record unemployment rate for adult women was 8.5 percent during the 1974-75 recession.

Payroll employment dropped by 220,000 in March, the department said, while total employment was "little changed for the third consecutive month" at 99.5 million.

Manufacturing industry lost 130,00 jobs, Norwood said, "bringing the total decline in factory jobs since last July to 1.2 million." The employment declines were spread across most of manufacturing industry, she said.

Yet another indication of the weakness in labor markets last month was a sharp drop in weekly working hours between February and March.

On Thursday the government reported that 623,000 people, almost a record, filed initial claims for unemployment benefits during the week ended March 20. A return to January levels of seasonally adjusted initial claims was noted by economist Alan Greenspan in his latest forecast where he said "there is no evidence in these data to suggest a recovery has gotten under way."

The proportion of the unemployed who have been out of work for three months or longer rose last month, Norwood said. Under the package of budget cuts passed by Congress last year, fewer people will become eligible for extended unemployment benefits than would otherwise have qualified.

The Congressional Budget Office calculates that 2.7 million unemployed who would have qualified for extended benefits in fiscal 1983 will be denied them because of the change, saving the federal government $3.1 billion.