Federal regional councils, the little-noticed offspring of Richard M. Nixon's brand of federalism, became a casualty of the federalism of President Reagan last week, when he signed an executive order sending them into oblivion.

The 10 councils were made up of the top regional officials of 10 federal agencies, who met to coordinate the administration of grant programs, regulatory efforts and a variety of other activities. At the end, the councils included representatives of the Environmental Protection Agency and all Cabinet departments except State, Defense, Treasury and Commerce.

"They've just outlived their usefulness," said Ron Peters, a senior employe at the Kansas City regional office of the Department of Transportation. Peters' boss, Patricia Keyes, is chairman of the regional council in that area.

"Their usefulness is pretty much tied to how the White House is going to use the councils," he said. "If there are federally centralized programs, you want a strong regional voice to encourage that sort of thing."

But with the Reagan administration's emphasis on returning more power to the states, he said, the number of things the regional council had to coordinate was dwindling. "I think the councils will fade into the sunset very peacefully," he said.

"The idea originally was to establish a coordinating mechanism in the field when the federal grant programs were being expanded," said James F. Kelly, who heads the Intergovernmental Affairs Division of the Office of Management and Budget. Kelly said federal officials wanted "to assist state and locals in understanding programs and applying for them."

"Many of these grant programs had similar purposes. The regional council was bringing the agencies together to educate the states and locals and minimize the overlap and dislocation," Kelly added. "But now the emphasis is on providing the states and locals with the maximum opportunity to interpret statutes and administer the programs the way they see fit."

Since the councils were made up of officials that hold other federal jobs, and the panels used only part-time or borrowed staff from other federal offices, they had no official budgets. Thus their departure will not be marked with the deletion of a line in the administration budget.

The coordinating work they did will continue, Kelly said, even though the formal structure no longer exists. When several agencies are providing funds for a specific project, the agency providing the most funds will become the lead agency, and will be responsible for communicating with local officials and ensuring that there is no overlap.

When President Nixon announced the councils' creation as one of his first acts in office in 1969, the White House issued a directive saying they "can make it possible for the federal government to speak with a single voice in its dealings with states and localities, with private organizations and with the public."

According to critics, however, the councils were accorded so little power that they were an ineffective vehicle for overcoming traditional interagency jealousies and turf fights.