WASHINGTON, April 25  Concerned about the growing dependence of the nation’s spy agencies on private contractors, top intelligence officials have spent months determining just how many contractors work at the C.I.A., D.I.A., F.B.I., N.S.A. and the rest of the spook alphabet soup.

Now they have an answer. But they cannot reveal it, they say, because America’s enemies might be listening.

Ronald P. Sanders, chief human capital officer for the director of national intelligence, said that because personnel numbers and agency budgets were classified, he could not reveal the contractor count.

“I can’t give you anything that would allow you to impute the size of the I.C. civilian work force,” Mr. Sanders said, using shorthand for “intelligence community” in a telephone briefing that covered everything about the contractor survey except its core findings.