In his 22 years as public relations director of the Labor Department, John W. Leslie built a solid reputation as a thoroughgoing, dispassionate professional who did well by Republicans and Democrats alike.

Therefore, it was no surprise when the National Association of Government Communicators named Leslie the recipient of its 1981 Communicator of the Year Award.

The surprise came late last week when the normally reticent Leslie, 57, used his acceptance speech to blast the Reagan administration in general and Labor Secretary Raymond Donovan in particular.

The communicators group "told me I could say anything I wanted," Leslie, who now is employed by The Kamber Group, a Washington-based labor lobby, said later. "So I told them what a lot of my former career government colleagues have been telling me, and what I have been feeling, myself."

After serving 32 years in the Labor Department, 10 of them before becoming public information director, and working for 12 successive secretaries of Labor in that position, Leslie said he left under the Reagan administration because "in the six months that I served . . . during this administration, no one asked me what I did, what my office did, who we served, why we existed, or what would happen if we disappeared."

Leslie said, "I sat for six months and watched a department in which I had worked most of my adult life systematically dismantled. I watched programs to serve and protect working people, which I had helped develop and promote, be slowly strangled or gutted." He said he began "to understand . . . how those of sensitivity and understanding must have felt when the barbarians sacked Rome.

"I claim, without qualification, that the efforts today throughout government to cut public information and public affairs activities are based not on a desire to save money, but are a cynical attempt by this administration to cover up efforts to destroy programs and services people want and need."

Leslie's speech has been circulating among some department careerists who agree with his position and who find some solace in the idea that one of their own, so to speak, can criticize the administration publicly without fear of retribution. But Reagan-Donovan loyalists such as Earl Cox, who holds Leslie's old position, understandably are unhappy.

"I regret that Mr. Leslie feels he was mistreated," Cox said last week. "No effort was made to sidestep him. Frankly, I was surprised by his remarks."