CORONADO — Mexican President Carlos Salinas de Gortari arrived in San Diego County Saturday and argued forcefully for his vision of a free-trade future linking Mexico, the United States and Can ada in a vast regional market.

"Investment and trade will offer benefits for each nation in the world of the 21st Century," Salinas told guests at a Coronado luncheon sponsored by the Center for U.S.-Mexican Studies at UC San Diego.

The president spoke during the first day of a three-day swing through California that is slated to conclude Monday, when he is scheduled to inaugurate a much-lauded exhibit of Mexican art at the Los Angeles County Museum of Art. It is his second visit to California since becoming president almost three years ago.

After his 10-minute address, Salinas met privately with Gov. Pete Wilson, whose administration views a prospective free trade regimen with Mexico as a financial bonanza for California, which shares a 140-mile-long border with Mexico. Trade between Mexico and California topped $8 billion in 1989, the last year for which figures were available.

In an issue of particular interest to the San Diego area, Salinas gave no definitive answer when asked after the lunch about the possibility of a joint airport linking San Diego and Tijuana. The concept has gained currency in the region but it has also engendered intense opposition from residents fearing increased noise, traffic and other problems.

A joint airport is still being studied, noted Salinas, who pointed out that Mexican authorities and private investors are now pumping some $300 million into improvements at Tijuana's Gen. Abelardo L. Rodriguez International Airport.

The Tijuana facility, Salinas said, "will become one of the most important airports in the whole nation," a response that some immediately interpreted as a strong indication that Mexican officials were more interested in increasing capacity at the Tijuana airport than embarking on a joint mega-project with San Diego.

The president's visit is viewed in part as a lobbying effort on behalf of the proposed North American Free Trade Agreement, details of which are now being ironed out by negotiators from the United States, Mexico and Canada. The prospective accord would reduce or eliminate tariffs, import fees, and other international trade barriers.