An apparent lack of planning has sent residents of Reston, the highly touted planned community in western Fairfax County, back to the drawing board.

According to findings released yesterday, there is a "critical need" for more child day care services for those who live and work in Reston, one of the county's centers of high technology industries.

A preliminary study conducted for the Reston Area Child Care Consortium, Inc., a coalition of 20 businesses formed to explore corporate-sponsored day care centers, found that in 1985, there were no spaces in licensed day care centers in Reston for about 30 percent of the children under age 5, or about 500 children.

The study also found that for 5,150 children ages 5 to 14 who need child care services before and after school, only 453 slots were available in child care centers and school-sponsored programs.

While current plans call for 147 day care slots to be added in Reston in the next two years, the study forecast that by the year 2000, about 2,600 new slots will be needed because of expected increases in population and new businesses.

"There is a tremendous need" for more child care services, said Rep. Frank R. Wolf (R-Va.), adding that "corporate leaders have an obligation to participate" in forming and financing child care centers. He said studies show that businesses that provide child care services for their employes also benefit through increased production levels, higher employe morale and lower absenteeism.

The Reston consortium, which includes the Arthur Young Inc., accounting firm, Unisys, Reston Land Corp., Tandem Computers Inc. and the Fairfax Hospital Association, is studying the feasibility of corporate-sponsored child care centers in Reston.

Information released yesterday was the first half of a $23,000 study of the issue. The second half, which will map out a plan under which businesses and parents would form partnerships to open and operate child care centers, should be completed by early fall, officials said.

No estimates were available on how much the program might cost.

Harry May, past president of the Reston Board of Commerce who has been involved in studying child care issues in Reston, said yesterday that there was no way planners could have foreseen the urgent need for day care when Reston was being planned more than 25 years ago.

Citing the increase in single-parent families and families with two working parents, in addition to the booming residential and business growth in Reston, May said, "It wasn't an oversight in planning. I don't think it was something to be considered back then or even five years ago."