Men on horseback: Reagan, Portillo prepare to barter

If all goes as planned, the presidents of Mexico and the United States will gallop off into a beautiful sunset at the end of their meetings next week. The careful preparations being made by the American side for the summit meetings here between President Reagan and Mexico's Jose Lopez Portillo reflect the importance that Reagan places on the US-Mexican relationship.

As it is now set, the stage for the two days of meetings between the two leaders provides for differences to be submerged and agreements to be emphasized. US officials are arguing that while the two may disagree on tactics when it comes to Central America, for example, they share common democratic values and strategic goals.

There will be more than eight hours of talks, with plenty of time for disagreements between the two leaders to be taken up in private. There also will be time for a walk around Mr. Reagan's retreat at Camp David, Md., and possibly some horseback riding. Both leaders are skilled horsemen, and Mr. Lopez Portillo gave Reagan a beautiful white horse at their first meeting, held at the US-Mexican border five months ago.

The differences between the two nations are many-- over undocumented workers, Mexican food exports, Cuba, and El Salvador, to name a few. The two leaders are not expected to resolve those differences in two days of meetings. But each has something he can give the other. Reagan wants to be seen as handling relations with Mexico in an effective manner. It now is a major oil exporter and the third-largest trading partner of the United States. Lopez Portillo is approaching the end of his six-year term in office, and he wants to demonstrate that he knows how to deal with Mexico's formidable neighbor to the north.

A key question is whether Reagan will agree to attend the meeting in Mexico of more than 20 world leaders, set for next October, which Lopez Portillo is arran ging. This could be the crowning achievement of the Mexican leader's career. For Reagan not to attend would be a blow. But the meeting is intended to discuss economic issues between the industrialized and developing nations. The Reagan administration is reviewing these issues at the moment but has left the clear impression so far that it opposes making any significant economic or financial concessions to nations of the so-called third world.

One danger for Reagan, as some administration experts saw it when the idea was first proposed, was that this major North-South summit, the first of its kind, might either throw Reagan into embarrassing confrontations or raise unrealistic expectations among developing nations.Among those to be represented at the meeting are leaders from nations as diverse as India and Yugoslavia, Nigeria and Algeria, and France, West Germany, Japan, and the United Kingdom.

But one administration official said Reagan will go to the unprecedented Mexico meeting, contrary to advice given earlier by some of his experts. For one thing, Mexico promises to create a congenial atmosphere that will avert confrontation. Informal talks are to be held among the leaders, with no communiques or agreements to be issued. The Soviets apparently will not be represented. They seem to feel no responsibility for North-South problems. Cuban President Fidel Castro apparently would not attend, thus avoiding another potential embarrassment for Reagan.

Reagan's willingness to go to this meeting could indicate new flexibility on his part vis-a- vis the developing nations. It also may be one more indication of the President's current ef- forts to treat the Mexicans as equals.

Reagan seems to recognize the importance the Mexicans attach to protocol and style. The President has twice dropped in unexpectedly to say a few words of greeting to recent Mexican visitors to the White House. The appointment of his friend, former movie actor John Gavin, as ambassador to Mexico may prove to be less of a mistake than it seemed at first, when it set off Mexican grumbling. Some Mexicans now say that the important point is that Mr. Gavin has the President's ear. And the tall, Spanish-speaking Gavin himself has so far shown a sophisticated command of the nuances in an often difficult relationship with Mexico.

Reagan has furthermore acceded to the Mexican desire for full consultation between the two countries, including frequent meetings between leaders. Officials say the personal "chemistry" between Reagan and Lopez Portillo holds much more potential for growth than did the sometimes strained relations hip the Mexican leader had with President Carter.