Top Mexican and U.S. officials today spent the first day of two days of high-level meetings discussing "all of the principal issues in Mexican-American relations," such as Central America, trade, debt problems and immigration, a senior administration official said.

Although little was said publicly about the two nations' differences over Central American policy, Secretary of State George P. Shultz and his Mexican counterpart met alone for more than two hours in the morning to discuss that issue and spent another two hours on the subject in the afternoon, the official said.

The official would not say whether the two nations moved closer together on the issue but added that it was a "very good discussion, very much in depth," which would continue tomorrow.

He said Mexico "would very much like to have support for its approach, which tends more toward step-by-step talks," while the United States is impressed by how difficult it is to make steps when there is so little trust among the nations in the region.

The Mexicans support the Sandinista government of Nicaragua and have urged negotiations between the U.S.-backed government of El Salvador and leftist guerrillas there. The Reagan administration, which opposes both the Sandinistas and Salvadoran negotiations, is known to feel that Mexican attitudes toward both are a hindrance to U.S. policy and to hope that increased economic cooperation during Mexico's time of need will be an incentive toward more cooperation in foreign policy.

At the opening session, the six Cabinet ministers--three on each side--emphasized the importance of economic and other ties between the United States and Mexico, Washington's third largest trading partner. Mexican Finance Minister Jesus Silva Herzog said that the success of Mexico's economic program will depend to a great extent on what happens to the U.S. economy and to U.S. interest rates. Shultz said the United States "fully understands the difficulties through which Mexico is now going."

With their economy in grave trouble after last year's financial crisis, Mexican officials today stress the importance of trade and economic relations with the United States. The United States has in turn been hurt in recent months by a sharp drop in Mexican imports. Foreign Minister Bernardo Sepulveda today said, "Mexico will only be able to maintain its imports insofar as it generates the means to pay for them."

The Mexicans are pushing for a trade agreement with the United States that would allow easier access to U.S. markets for Mexican goods. The Mexican government specifically requested that Commerce Secretary Malcolm Baldrige come on the trip with Shultz and Treasury Secretary Donald T. Regan.

The two days of talks in Mexico City mark the first high-level U.S. contact with the four-month-old government of Mexican President. They should pave the way for a meeting later this year between President Reagan and de la Madrid, officials said.

U.S. officials have stressed that the talks are aimed primarily at exchanging views and developing personal contacts between the U.S. Cabinet members and their Mexican counterparts.

"We have not brought our checkbook," one Treasury official said. Regan told reporters on the plane that while Mexico now "needs no additional financial help . . . that's no guarantee that some assistance might not be called for in the future."

A senior administration official said later that the two finance ministers had discussed Mexico's debt problem--the nation has more than $80 billion in foreign debts--and likely will continue the talks over how to reach agreement between Mexico and its bank creditors.

On Central America, Shultz said he did "not know of any new initiative." He added, however, "We're certainly going to discuss these issues . . . . If we find something that we think will be useful, we'll be ready to pursue it."

Sepulveda today acknowledged the U.S.-Mexican policy differences over Central America and said that an approach between the two views was "not only desirable but an urgent condition to bring about a lasting solution to the troubled region."

Shultz said he hoped Mexico's "long experience" in the region "will serve the cause of justice and peace," adding that there were "few voices we respect more than Mexico's." On the plane, the secretary of state referred again to "growing Soviet-Cuban influence in Nicaragua," and today said that both Mexico and the United States recognize that Central American nations are "capable of governing themselves without outside interference."

Mexico last year reached agreement with the International Monetary Fund on an austerity program to reduce its dependence on foreign cash in return for an IMF loan. U.S. Treasury officials said today that the nation now is meeting its financial commitment. This, however, largely reflects the deep slump in the economy, which has cut imports.