Education Secretary T.H. Bell charged yesterday that labor union critics of President Reagan's education policies had "exaggerated the facts about alleged budget cuts" and said that the unions, not the president, were "misleading" the public.

Bell said at a news conference that a union report on education spending, issued Thursday, had "more inaccuracies than anything I've seen in a long time." He said it was motivated by concern that the president was making political gains by "taking to the stump" about merit pay for teachers and other education issues during the past few months.

"Our opponents have considered education to be their sandbox," Bell remarked, "and they're angry like a spoiled kid that somebody else has climbed in."

The report, issued by the public employe department of the AFL-CIO, details cuts in federal education spending in each of the nation's 435 congressional districts. It covers two major programs--Chapter I (formerly Title I), aimed at children of low-income families, and Vocational and Adult Education.

The union figures show cuts in service levels of about 20 percent, with inflation factored in, since Reagan took office.

Yesterday, Bell said the unions' statement that 750,000 children have been dropped from Chapter I was untrue and that both appropriations and participation in the program have gone up slightly over the past three years. Bell said that although federal aid for traditional vocational programs has been curtailed, the administration has supported increases in federal student aid and job training programs, which he said better serve the same purposes.

Later, Tom Fahey, a spokesman for the AFL-CIO group, said the unions "stand behind our numbers . . . . The data and the assumptions underlying our report are open to public review. We know they can stand up to public scrutiny."

Bell acknowledged that the Reagan administration had sought much less federal spending on education than Congress approved, but said this was part of an effort to curb inflation and increase efficiency. Under the budgets passed by Congress and signed by Reagan, he said, U.S. Education Department spending has gone up from $14.1 billion in 1980 to $15.4 billion this year.