The nation's manufacturers continue to order machine tools at a lively rate despite growing evidence that the overall economy is slowing.

Machine tool orders totaled $469.2 million in May, up 1.6 percent from $461.7 million in April and 32 percent higher than $354.9 million in May 1978, the National Machine Tool Builder's Association reported.

Industry executives say inquiries and requests for price quotations continue strong, indicating that the healthy order pattern will continue for a while. However, most expect a leveling off in the order rate, and some foresee a modest decline from the high rates of recent months.

Orders for the first five months of 1979 were 41 percent higher than a year earlier, the association said. And orders have been running 60 percent higher than the industry's shipping rate.

George J. Becker, president of Giddings & Lewis Inc. of Fond Du Lac, Wis., said the recent "level of orders is unsustainable." However, he said "orders continue at an excellent rate," a pace that "has confounded many of the expert forecasters. We see continued strength for the near term," he added.

Machine tool executives say there are a number of reasons why orders remain high even though the economic outlook is decidedly softer than it was six months ago. For one thing, capital goods traditionally track the business cycle, rising more slowly in the early stages of an economic recovery but then continuing strong after consumer product sales turn down, they say.

And this time there are some special factors, according to James A. D. Geier, president of Cincinnati Milacron Inc., the largest machine tool producer. The auto industry is reequipping its plants to make smaller, more-fuel-efficient cars, and that program can't be halted because of slower auto sales, he said. The government is demanding lower fuel consumption, and smaller cars are in demand anyway because of the gasoline shortage, he explained.

A new generation of lighter and more efficient aircraft also is being developed in response to rising jet fuel prices, and that program also will continue in spite of a probable weakening in the overall economy, Geier explained.

Firms building coal-mining machinery, construction and materials-handling equipment and non-electrical machinery "all indicate that they are committed to capital spending regardless of the economy," Becker said.

Machine tool shipments totaled $317.7 million in May, up 4.1 percent from $305.1 million in April, and 24 percent higher than $255.7 million for May 1978, according to association figures.

Producers say they have been hampered in their efforts to increase production by shortages of skilled machinists and other technical and skilled personnel. Machine tool producers are making plant additions and ordering new equipment to raise their capacity, but it takes time to get that capacity into production.