Mexico is considering joining the General Agreement on Tariffs and Trade (GATT) -- an action it refused to take six years ago -- so it can participate in a new round of global trade talks being pushed by the Reagan administration, Commerce Secretary Hector Hernandez said yesterday.

The decision to join the 90-nation organization that regulates world trade is considered politically sensitive by the government of President Miguel de la Madrid. But it has won strong support from influential Mexican business leaders, who have been spreading that word this week among members of the Reagan administration and on Capitol Hill.

"Now the mood and the public opinion is to review again our international trade relationship," Hernandez said during an interview.

"Public opinion is beginning to think that it's time to reopen discussions about the participation of Mexico in GATT," added the Mexican official, who was in Washington to receive an award with former U.S. trade representative William E. Brock from the Mexico-U.S. Chamber of Commerce.

"It's a huge turnaround for them in the last six months or a year," commented one U.S. trade official.

Nonetheless, U.S. Trade Representative Clayton Yeutter was reported to have warned Hernandez that the terms for becoming a GATT member are likely to be stiffer than they were in 1979, when Mexico abruptly pulled away from joining the multilateral trade group.

While Mexico is saddled with a $95 billion debt, the second highest in the world, and suffers from the global glut of oil that has cut income from its leading export, the United States believes Mexico has developed a strong-enough industrial base over the past six years to do without major concessions from GATT rules.

Hernandez said the question of Mexico joining GATT currently is before the nation's Senate, which will issue a report this month. "Personally, I think it will be positive," said Hernandez.

One factor behind the Mexican decision is the likelihood that a new round of world trade talks will be held, possibly as early as next year. Mexico did not take part in the last global trade talks and, according to observers here, lost out on some of its benefits.

"We think this new round, in many aspects, will shape the future of international trade," he said. "We think that as one of the leading underdeveloped countries, we have something to do in the new round."

While these talks are opposed by many less-developed countries, led by India and Brazil, they are being pushed by the United States, the European Community and Japan. Yeutter has warned that the Reagan administration will not allow the opposition of a few nations that play a relatively small part in world trade to block talks dealing with areas presently not covered by GATT rules, such as services, high technology and agriculture.

The shift in Mexico's attitude toward joining GATT coincides with moves by the de la Madrid government to liberalize its rules governing 65 percent of the value of all its imports, Hernandez said.

One reason for import liberalization, the Mexican offficial said, is to help the country increase its exports. "If the Mexican industry is able to compete in its own market, that will guarantee that it will be able to compete in foreign markets," he said.

Hernandez, echoing the view of all Mexican officials when they visit Washington, complained that interest on Mexica's huge debt, which amounts to as much as $12 billion a year, hurts its economic growth.

He called for expanded U.S.-Mexican trade, which reached $30 billion last year. Mexico has held a surplus in bilateral trade since 1982; last year, the surplus amounted to $6.3 billion.

"The Mexican market is important to the United States, but we need to get the means in order to import," said Hernandez.

Mexico last year signed an agreement with the United States to eliminate export subsidies, which has helped it fight unfair trade cases brought by U.S. manufacturers.