The Boeings and the Lockheeds are an obvious presence here at the 33rd Paris Air Show, but scores of lesser known American companies are also seeking to expand their sales in the international aviaton and aerospace arena.

Many, including newcomers to the show, say they have been successful and expect to increase their export business substantially.

"It looks like we've sold six airplanes," said Richard P. Maccoon, president of Mr. RPM Agri-Products, a company headquartered in Van Nuys, Calif.

The planes are only the first part of the sales for Maccoon, whose company sells complete plans for the planes to Third World countries. The company brings people from their home countries to the U.S. where they are trained and sent back with visual aids on how to put together a factory that produces and services the agricultural aircraft. The planes are used for spraying and fertilizing, but the technology used in the plants can be converted easily to production of buses and vehicles, according to Maccoon.

Buyers take the plane first to see if they like it before commiting themselves to the factory. "Who wants to build a manufacturing plant that produces a lousy product?" Maccoon asked.

The $280,000 in sales he wrote at the show more than justified the expenses, he said. Maccoon and other businessmen who are new to the show are charged $2,000 for a booth in the U.S. pavillion by the Commerce Department. Exhibtors who have participated before are charged $3,500.

E.D. McDonald, president of Edmac Associates Inc. of Rochester, a company that produces electronic aircraft equipment for sales to air forces and navies, expects to increase significantly his export business - now 20 percent of his $8 million annual sales - because of the show.

"I met a lot of people who saw our products for the first time and asked for quotations, and some asked about representing us in parts of the world not yet represented," he said. He was so happy about his contacts he reserved a place in the next show two years from now. "I think we all have to export more to pay for that oil," he explained.

J. Hall, vice president for marketing of Bellanca Aircraft Corp. of Alexandria, Minn., a manufacturer of small planes that sell between $18,000 and $30,000, said contacts made for five good distributors around the world during the show could mean about $3 million in sales to the company. "It's been excellent as a meeting place," he said.

All together, 106 U.S. cmpanies had booths in the U.S.pavillion in addition to the two to three dozen major American companies that had larger displays and hospitality "chalets" at this massive show. More than 500,000 persons were expected to visit the show - which ended today - with more than a third representing business and government buyers from all over the world.

The smaller companies actually make more sales at the show than the larger ones, businessmen say. "You don't walk in here and buy a 747," a Boeing official pointed out. "It takes a little more work."

This is the last time the U.S. can use the pavillion it built almost 10 years ago unless it negotiates a new lease - something government officials here assume will take place. "It's inconceivable that the U.S. wouldn't be in the show again," said Hellmuth L. Kirchschlager, a Commerce Department official who has served as director of marketing activities for the show. "Sales in this industry are the second largest in export sales next to agriculture and will generate $11.1 billion toward a favorable balance of trade this year," he said.

Senate Commerce Committee Chairman Howard W. Cannon (D-Nev.) who served as the president's representative to the show, said he strongly supports U.S. export efforts here. "It is the one showcase where everyone can set up their wares and show them to a lot a foreign customers at one time," he said.

"If we were not there it would be a conspicuous absence for foreign buyers out with legitimate shopping lists for their needs."