A congressional study commission, after months of wrangling and one important change in membership, recommended yesterday the "complete elimination" of antitrust immunity for trucking firms in setting rates to haul freight.

The 6-to-4 vote of the Motor Carrier Ratemaking Study Commission came on a staff recommendation that was unchanged from one offered in December, but which died on a 5-to-5 vote then. In the meantime, former Sen. Howard Cannon (D-Nev.), who had lost his bid for re-election, was replaced on the commission by Sen. Barry Goldwater (R-Ariz.).

Cannon, long-time chairman of the Senate Commerce Committee, voted with the trucking companies and against the proposal. Goldwater voted with Sen. Bob Packwood (R-Ore.), the commission chairman.

The central issue is the continued existence of rate bureaus, a collection of trucking companies that sets freight rates for both single-carrier and interline truck shipments. The bureaus have prospered since they were granted antitrust immunity in 1948.

Under the trucking deregulation act, that immunity will expire July 1, 1984, for single-carrier shipments. Congress will have to act before the bureaus are abolished for interline shipments. The commission has now recommended that it do so.

The commission findings, contained in a 22-page document, strongly support the deregulatory approach to transportation pricing and market selection that has gathered steam over the past six years. The commission found that since new legislation has made it much easier for truckers to enter or leave markets and to set rates pretty much as they please, there is less need for rate bureaus.

However, the commission said, "The overall rate level" paid trucking firms "is higher than it would be in the absence of collective rate-making. Collective rate-making creates a climate which nurtures growth in wages substantially in excess of labor productivity gains."

Commissioner Steve Murphy, senior vice president and general counsel of Yellow Freight System Inc., fought the proposal on the grounds that rate bureaus provide stability to the industry, but do not act as a floor on prices.