Walter B. McCormick Jr., the new president of the American Trucking Associations, is developing an ambitious agenda to prevent additional taxes, push for ''common sense'' regulations and ''fight night and day'' for higher highway spending.

Mr. McCormick's talk Friday at the Transportation Table sponsored by The Journal of Commerce and Traffic World magazine was his first major appearance since taking over the ATA three months ago. He succeeded Tom Donohue, who left to head the U.S. Chamber of Commerce.In the tax arena, he urged Congress to reduce the estate tax that ''is destroying family-owned trucking companies and robbing us of the next generation of truckers.'' Two other tax targets are the removal of remaining weight/distance taxes and federally approved fees for ''toll-free'' inbound telephone calls.

ATA's support of higher highway funding can create safer, better maintained roads, he said. He noted that an additional $10 billion annually in road spending would add 500 miles of new highway.

Regulatory issues include reforming hours of service laws and blocking national standards for workplace ergonomics.

Mr. McCormick talked tough on truck size and weight issues that have sparked sporadic clashes with the railroads.

Noting that an amendment to restrict triple trailers was withdrawn from Congressional consideration, Mr. McCormick said that ''on truck size and weight, ATA is speaking with one voice. No rollbacks. We are drawing a line in the sand. This isn't a battle over safety. It is a battle over economics. It is an attempt by our economic competitors to reduce trucking's productivity.''

Mr. McCormick also pledged to work with a variety of highway safety groups, including the Insurance Institute for Highway Safety, Mothers Against Drunk Driving and Public Citizen.

He promised ATA would be a ''leaner, more efficient and member-responsive'' organization with closer ties to state trucking groups and a more vigorous Washington presence. He said that after two years of losses and three years of membership declines - a 10 percent staff reduction brought the group's budget into balance.

Mr. McCormick pledged renewed efforts to boost membership and build unity.

''There is increasing frustration within our industry over the fragmentation of policymaking,'' he said. ''There is anger that ATA was taking members' money and living the high life, a life different than the lives most truckers lead.''

''What we are about in our federation is the process of forging consensus,'' he said. ''Forging consensus is never easy. It is tough. You cannot have unit without consensus, and we are going to have unity in the trucking industry. We are going to speak with one voice.''