Machine tool orders fell sharply in December from the record levels of October and November, but industry executives think it was a one-month blip rather than an indication of softening capital spending plans.

Machine tools are complex machines used to shape most metal parts from oven doors and other consumer products to electric power and turbines and industrial gears. Orders for machine tools therefore are an advance indicator of capital spending in manufacturing but industry officials stress that timing of a few large orders can cause monthly fluctuations that confuse the basic trend.

Orders in December dropped to $324.9 million, 26 percent below the $441.1 million of November but were 1.9 percent higher than the $318.7 million of the year earier month, according to the National Machine Tool Builders' Association.

However, looking at the fourth quarter as a whole, orders were a record $1.18 billion, up from $1.03 billion in the third period and $1.13 billion in the second quarter, the previous high. Industry officials think the unusually high orders in October and November may have borrowed ahead from December but that the fourth quarter as a whole provides a fair indicator of business trends.

December orders for lathes, grinders, milling machines, machining centers, boring mills and other machines to shape metal by cutting fell to $246.2 million, 30 percent below November's $352.9 million and 1.7 percent lower than the $250.4 million of December 1977.

Orders in December for metal-forming presses and other machines to shape metal with pressure were $78.8 million, down 11 percent from $88.2 million in November but were 15 percent higher than the $68.3 million of a year earlier, the association said.

"Our orders continued good through the end of 1978 and are very good so far in January," a spokesman for Cincinnati Milacron Inc. said.

Machine tool producers are watching a couple of national trends that could be a threat to continued strong sales. The most immediate problem is high interest rates which may make financing a purchase more difficult for some buyers. The second is the concern about a downturn in the overall economy later in the year which would lessen the requirement for added capacity.