The nation's civilian unemployment rate in April was unchanged at 7.3 percent for the third consecutive month although manufacturing jobs continued to disappear as a result of the economic slowdown.

Jobs in manufacturing industries declined by 45,000 in April, the Labor Department reported yesterday. They have dropped by 130,000 since January as economic growth slowed to a crawl during the first three months of the year and as imports continued to displace domestic-made goods.

Overall, the number of employed declined by 174,000 to 106.9 million in April, and the number of unemployed was unchanged at 8.4 million for the third consecutive month, according to a Labor Department survey of households. A separate survey of businesses showed jobs rose by 217,000 last month even with the decline in manufacturing.

The unemployment report came as President Reagan met with leaders of six other industrial nations in Bonn to discuss ways to improve the world economy. Reagan several months ago had boasted to the Europeans -- whose unemployment rates have risen -- of the sharp drop in the unemployment rate here created by what he called the "Great American Job Machine."

However, the labor market picture has changed little since last fall, and the unemployment rate, while bouncing up and down for several months, has dropped only slightly from 7.5 percent last May. Economists yesterday said the unemployment report confirmed predictions that the economy may be headed toward a growth recession, when too few jobs are created to prevent the rate from rising.

White House spokesman Larry Speakes disagreed, saying that "the nation's economy remains strong, and -- despite the fact that the unemployment rate has not fallen in three months, we still see total employment in this country running at all-time highs."

Employment was higher in March at 107.1 million persons with jobs.

Economists blamed the stagnant unemployment picture on the overall slowdown in economic growth since last fall and the continuing influx of goods from abroad, which have cut into the market share of many manufacturers, helped reduce their profits and prevented them from hiring more workers.

"We have some serious problems, clearly," Janet L. Norwood, commissioner of the Bureau of Labor Statistics, told the Joint Economic Committee yesterday. "It's quite clear that we have been stuck at this level for many, many months." Norwood said the manufacturing sector was "extremely weak."

The nondurable manufacturing industries have recovered only about two-thirds of jobs lost during the recession, and makers of durable products -- those that generally last three years or more -- have recovered slightly more, Norwood said. In contrast, jobs in the services-producing industries have risen by 663,000, and employment in retail trade increased 152,000 since January.

David Jones, chief economist for Aubrey G. Lanston & Co., said that the increase in payroll employment was much smaller than many analysts had expected, suggesting that income growth in the future will slow, leading to a possible growth recession by the end of the year.

"More important is the decline in manufacturing employment," Jones said. "Since late summer the drag on the economy from the deepening trade deficit is becoming more pervasive. This is more confirmation that the U.S. economy is being deindustrialized" by the influx of imported goods and foreign parts in domestically assembled products.

"The slow overall employment growth and the accelerated deterioration of employment in the manufacturing sector support projections . . . that the first-quarter weakness of the economy is continuing in the second quarter," said Jack Carlson, economist with the National Association of Realtors. "While nonfarm payroll employment grew a seasonally adjusted 217,000 from March to April, this was down from the 278,000 average gain in each month of the first quarter." The largest job loss in manufacturing was in the high-technology sector, particularly in electrical and electronic equipment production. Employment in those industries fell to the level of last summer, about 2.3 million, the Labor Department said.

Additionally, the average weekly hours of nonsupervisory workers on private nonagricultural payrolls declined 0.1 hours in April. Hours for factory workers declined 0.1 hours, but overtime work increased 0.1 hours, the Labor Department said.

Average hourly earnings of nonsupervisory workers increased 0.5 percent in April. Average weekly earnings rose 0.2 percent, Labor said.

The unemployment rate rose for whites from 6.2 percent to 6.3 percent and the rate for blacks rose from 15.2 percent to 15.3 percent. The unemployment rate for teenagers dropped sharply from 18.2 percent to 17.7 percent.