Employers in the trucking and auto manufacturing industries are seeking additional concessions from unions that have already sacrificed billions of dollars in wages and benefits in national contracts negotiated this year.

The push for more givebacks is being made at the local level, where labor and management are trying to work out contracts at companies not covered by the national pacts and where others are trying to draft supplemental agreements on matters that could not be handled in national bargaining.

For example, nearly 600 companies not covered by the new National Master Freight Agreement (NMFA) in the trucking industry are trying win contracts from their workers represented by the Teamsters union. The contracts would eliminate cost of living allowance (COLA) payments and freeze or roll back wages.

The 37-month-long NMFA, ratified by the Teamsters' rank and file March 31, freezes basic hourly wages for union-represented workers for the next two years. But the agreement allows covered workers cost-of-living raises, the first of which, 47 cents an hour, was due April 1.

Some of the 2,000 carriers under the NMFA are refusing to make the scheduled COLA payments because unionized companies not covered by the agreement would enjoy a labor cost advantage if they win a wage freeze plus a COLA cut.

Trucking associations in Ohio and Michigan last month asked member companies to put COLA payments in escrow accounts until local bargaining is resolved. But officials of the Ohio Motor Carriers Labor Relations Association later rescinded that directive, saying the association instead would seek an "Ohio rider" to the national wage agreement.

Teamster sources reached in Ohio yesterday said the rider sought by the state association would knock $1.05 off the current average hourly wage of $13.31 paid to truckers and freight handlers in the Midwest. Spokesmen for the Ohio motor carriers group could not be reached for comment.

Last month, in a local agreement, the Dallas-based Spector Red Ball Co., a common carrier, won a 15 percent wage cut from its workers. The company preferred to call the concession a "wage loan" by workers to help the company over financial rough spots. The "loan" would be repayable if and when economic conditions improve.

Although trucking industry bargaining is often difficult, the latest developments have created "unbelievable chaos," Bob Masters, a spokesman for the dissident Teamsters for a Democratic Union said yesterday.

"We have some people paying COLA and some who are not. There's also a question of whether or not companies covered by the national agreement will receive substandard wage riders. All we have is unbelievable chaos," Masters said.

In the auto industry, General Motors Corp. is preparing to open local negotiations at its 147 domestic plants. GM, the nation's largest auto maker, won $2.5 billion in wage and benefit concessions in a 30-month national contract negotiated last month and signed last week.

In its local talks, GM is going after work rule changes that some industry analysts say could save the company an additional $2.4 billion over the life of the new agreement. That extra saving would put GM in a better position to reduce significantly the estimated $8-an-hour labor cost advantage now held by Japanese auto makers.

United Auto Workers union spokesman Don Stillman said in a weekend interview that the UAW supports efforts to do away with costly and inefficient work rules. Noting that the national agreement was ratified by a narrow 52 to 48 percent vote, he said any attempt by the company to seek major local concessions would meet strong resistance.

"The ratification vote just doesn't bode well" for deeper cuts locally, Stillman said. He said the possibility of local strikes has been diminished by the depressed state of the auto industry, in which 150,000 GM workers have been laid off.

Local unions failing to reach agreement would continue operating under current plant contracts until the national agreement expires Sept. 14, 1984, he said.