Mexicans no longer believe "there exists or can exist a special relation with the United States," ambassador-at-large Jorge Castanedo told a symposium here this week.

To its sorrow, Mexico has learned that the big power next door "will pursue big-power interests," said Castaneda, who suggested that his country should pay more attention to "medium powers" like Sweden, Canada, Nigeria, Yugoslavia and Venezuela.

The diplomat said a close U.S.-Mexican relationship still should be an objective of Mexican policy but "must not be seen as an end in itself" as has been the case in the past.

Castaneda's candid presention was part of an ambitious five-week symposium here on Mexico Today, sponsored by the Smithsonian Resident Associate Program and Meridian House International.

Audiences averaging about 300 have heard panel discussions by Mexican and American authorities each Monday night at the Pan American Union. Art exhibits, readings, lunches and courses for adults and children have been keyed to the symposium, which also is being held in eight over U.S. cities.

Castaneda, in a catalogue of what he considers wrong with U.S. attitudes toward Mexico, cited what he said is known here as "the Mexican drug problem," the traffic of narcotics across the border.

"Until you see it as a problem for Mexico, and not as a problem created by Mexico," there is little hope of mutual understanding, he said.

Listing such U.S. actions as the restriction of vegetable imports from Mexico and the most recent reduction of the immigration quota," Castaneda concluded: "So much for the special relation."

The previous Monday, president Victor Urquidi of the College of Mexico gave a biting analysis of Mexico's economic performance, contrasting the considerable economic growth with what he described as a failure to redistribute that added wealth.

Now the hope is the country's newly discovered oil wealth, said Urquidi, but the crucial issue "is developing a strategy for creating employment for the still rapidly increasing labor force."

A recurrent theme at the symposium has been Mexico's particular problems as an "intermediate" developing country. Abelardo Valdez, an American of Mexican origin who is now assistant administrator for Latin America, at the Agency for International Development, discussed the issue at one of the symposium lunches. The speeches were a first echo here for Valdez' until-now lonely call for more U.S. aid to Latin nations in "intermediate development."