The Reagan administration today promised protection to mayors and county commissioners fearful of being shortchanged when federal categorical aid programs are consolidated into block grants controlled by the states.

Health and Human Services Secretary Richard S. Schweiker, speaking to the annual meeting here of the National Association of Counties, said he could order tough audits and bring other pressure on states depriving local governments of their fair share of federal funds.

Schweiker also announced the formation of a task force of representatives of mayors, county officials, governors and state legislators to devise "remedy and grievance procedures" and help "smooth the transition."

"I think it's going to be the art of persuasion and the art of publicity that is going to make things work," he later told reporters.

Many of President Reagan's proposals for block grants have been significantly altered or rejected by the House and Senate, although many comparatively small education and health programs have been consolidated in budget bills.

Administation officials have tended to stress the advantages of increased flexibility in block grants and the discretion they give to government that is "closer to the people." Mayors and county officials, however, in many cases already battling with statehouses over taxing authority and the division of state funds, have repeatedly emphasized concerns about the federal block grants in White House meetings with Reagan. Schweiker's comments appeared to be a gesture aimed at soothing those fears.

In contrast to the cold shoulder given to big city mayors who had criticized the president's economic recovery program in their meeting here last month, the administration has been extremely solicitous of the National Association of Counties, sending not only Schweiker but also Housing and Urban Development Secretary Samuel R. Pierce, Agriculture Secretary John R. Block and Interior Secretary James G. Watt to speak. Also here representing the administration is Richard S. Williamson, senior White House liaison with state and local governments.

This attention appears to have been the result of the staunch support given to the White House by the group's outgoing president, Roy Orr, a conservative Democrat and commissioner of the Dallas County, Tex., government. Orr told reporters he had met with Reagan six times and gotten so many other invitations to meet with White House aides that he had to turn down two.

In contrast to the exuberant praise of the administration by Orr, however, the county executives and county commissioners meeting here expressed a number of concerns over the president's programs. They asked for guarantees in legislation that block grant funds going to the states would reach them and they called for restoration of cuts in federally aided programs for day care, job training and legal services.

There were nervous titters and knowing looks when Rep. Les Aspin (D-Wis.) told the officials that they would take the heat after the cuts had taken effect in their communities.

"You've got a very, very serious problem facing you politically because I think Washington is going to be well out of it . . . . My guess is that when this group meets again a year from now, and more so two years from now, there's going to be a lot of new faces."