President Carter yesterday named A. Daniel O'Neal, a member of the Interstate Commerce Commission since 1973, to be chairman of the nation's oldest federal regulatory agency.

O'Neal, whose selection by Carter was reported a month ago, succeeds George M. Stafford, who is expected to remain a member of the ICC at least until his current term expires on Dec. 31, 1980.

The 40-year old O'Neal was named to the agency by former President Nixon in 1973; his term expires at the end of 1979.

Since O'Neal already is an ICC member, his designation as chairman does not have to be confirmed by the Senate, where he long has had broad support.

A native of Bremerton, Wash., O'Neal was legislative counsel to Senate Commerce Committee chairman Warren Magnuson (D-Wash.) from 1967 to 1969 and later was transportation counsel to the committee, where he directed a major study of the Penn Central Railroad collapse.

In recent months, O'Neal has been a frequent dissenter to decisions by the ICC - including recent approval for a nationwide increase in bus fares.

However, O'Neal also has spoken out recently in favor of continued federal economic controls for industries under ICC jurisdiction - railroads, truck lines, bus companies, inland water barges and oil pipelines.

"Regulation will continue to be relied upon to accomplish many of the traditional public interest objectives," O'Neal told a transportation gathering in Los Angeles during the past fortnight.

He said ICC regulation could be "fairly described as a balancing operation," in which an effort is made to weigh needs of shipping companies and their customers, large and small.

This "balancing" operation will be the subject of congressional hearings this year on ICC regulation of the trucking industry and O'Neal said his agency's regulation of trucking since the 1930s has "provided an important element of stability for shippers."

The concept of requiring common carriers to serve the whole public "has always been important to industrialized countries" and opening up the trucking business to free entry could lead to reduced competition, he warned.

"Any substantial reductions in service or increases in rates might yield greater carrier efficiency and profitability but at a cost of significant adverse effects on many shippers and on the economy of the nation's rural areas," he declared.