The National Labor Relations Board intends to charge Honda of America with an illegal attempt to prevent the formation of a union at its motorcycle manufacturing plant in Marysville, Ohio, a board official said yesterday.

The NLRB's action follows a complaint against Honda by the United Auto Workers, which regards the Marysville plant as a crucial test of whether Japanese-owned auto plants in the United States will be organized or nonunion.

The Honda News Bureau made the following comment in Los Angeles: "We sincerely believe that we are not violating any laws in the United States and are not interfering with any rights of our associates."

The motorcycle plant, now employing 200 workers, is Honda's first manufacturing facility in this country. The first Japanese-owned automobile plant in the United States will be built at the same location in the next few years, Honda has said.

A dispute over caps triggered the complaints against Honda.

A UAW supporter showed up for work this summer wearing a UAW baseball cap and union button and was told by company officials to take them off, the UAW says. The employe did as he was told.

Honda says it merely was enforcing a dress code which requires workers to wear white uniforms with their names and Honda's embroidered in red letters, a measure to improve teamwork, according to the company.

"If they want to wear a hat, too, it has to be a Honda hat," a company official said yesterday, "not a Kawasaki hat or a UAW hat." The dress code "has absolutely nothing to do with the UAW or any other union," the company contends.

UAW officials complain that the rule against caps, buttons or UAW T-shirts makes it harder for plant workers to identify union supporters, thus frustrating its organizing efforts.

The company also has been "misleading" employes by calling them "associates" and suggesting that they have a special relationship with management that is part of "the Japanese way," the UAW complained. A Honda spokesman said there has been little organizing activity at the plant, except for some distribution of UAW literature outside the gates.