The National Association of Manufacturers and other leading economic forecasters have sharply reduced their estimates for economic growth this year, but say they do not foresee a recession before 1987.

If the lower growth estimates are accurate, they pose a problem for the Reagan administration's attempts to reduce the federal budget deficit, because lower growth means higher outlays for some services and lower revenue from taxes. Office of Management and Budget Director David A. Stockman this week warned that reduced growth would mean more effort would be needed to reduce the deficit.

On the more positive side, the NAM and other major forecasters said that the rate of inflation will remain stable. The NAM forecast a CPI increase of about 3.5 percent this year, compared with the 3.3 percent rate for the first quarter.

Interest rates will decline by approximately half a percentage point this year before leveling off, the NAM said.

Some of the reductions in growth estimates are not surprising because economic activity in the first half of the year has been much lower than many economists expected, which would reduce the average for the year. These economists only changed their figures for the first half of the year, leaving second-half estimates the same.

However, other economists expect the economic deterioration to continue into the third and fourth quarters.

The NAM yesterday said it has dropped its forecast for growth this year from 3.8 percent to 2.4 percent from the fourth quarter of 1984 to the fourth quarter of 1985. The major reasons for the downward revisions were that businesses have misgauged consumer demand and are overbuilding inventories, and the trade deficit has continued to divert production away from domestic industries.

In addition, the Federal Reserve Board's monetary restraint last year and the subsequent increase in interest rates have imposed a drag on the economy, and a decline in monetary velocity has added to the downturn in economic activity, the NAM said.

That forecast compares with the administration's prediction of 4 percent growth from the fourth quarter of 1984.

"The result of this confluence of factors is that there is very little activity in the economy as of the current time," the NAM said in issuing its revised economic forecast. "Both consumption and investment spending are weak, while military spending by the federal government has not been sufficient to arrest the slide in industrial performance."

Wharton Econometrics recently lowered its expectations for economic growth for 1985 to an average of 2.6 percent from the 2.9 percent estimate made in April.

"The Wharton economic growth outlook for both 1985 and 1986 has been revised downward since last month," Wharton said in its newsletter at the end of May. The revision was made because of "the growing likelihood that federal government spending will be cut substantially relative to prior budget requests, the continued strength of the dollar even in the face of sustained interest rate declines, and a growing realization that the industrial core of the U.S. economy is extremely vulnerable to low-price foreign competition."

Wharton now forecasts lower second-quarter growth, with growth for the third and fourth quarters of the year about the same.

The Blue Chip Economic Indicators, a consensus forecast of 50 economists, this month lowered its expectations for average growth this year from 3.9 percent, according to a March survey, to 2.9 percent, largely because of slower-than-anticipated growth in the first half of the year and expectations of growth just slightly higher in the last half.

Stockman this week used the Blue Chip forecast, rather than the administration's figures, for estimating the budget deficit through 1988.

According to Jerry Jasinowski, NAM chief economist, the economy is expected to pick up only gradually during the last part of the year, and the civilian unemployment rate will remain essentially where it is, about 7.3 percent.

The NAM originally said growth would be 2.1 percent in the first quarter, 3.6 percent in the second, 4.1 percent in the third, and 4.6 percent in the fourth. However, in its forecast released yesterday, the NAM said that after the actual 0.7 percent rate in the first quarter, the economy would grow at a 2.2 percent rate in the second quarter, 2.4 percent in the third and 4.5 percent in the fourth.

Recession, if it hits, does not appear likely to occur until after 1986, and the most likely cause would be an uncontrollable buildup in inventories because of low demand, Jasinowski said.

Meanwhile, International Business Machines Corp. Chairman John F. Akers said yesterday his company had revised downward its forecast for economic growth from 3.7 percent to 2.9 percent.

"This disappointing economic performance does not result from a lackluster domestic demand, which I believe would support an annual gross national product rate of perhaps 4 percent," Akers said at a meeting with securities analysts. "It results primarily from the fact that too much of that demand is being met by imports -- massive increases in U.S. imports, fueled by the strong dollar."