Cancun, Mexico — The Cancun summit was a triumph of pragmatism over ideology. For one brief moment, leaders from 22 nations set aside differences to talk about such things as how to grow more food, how to produce more energy, and how to reduce trade barriers.
The give-and-take was described by many of those involved as remarkably free and relaxed.
But the United States, represented by President Reagan, yielded little of significance to third world demands. And if the Cancun spirit of pragmatism cannot be transmitted to other countries and officials throughout the world, Cancun will prove to be less of a turning point than it now seems to be.
For a number of leaders, not the least of them President Reagan, the summit in Cancun Oct. 22 and 23 was an unprecedented opportunity to learn.
''The process of educating President Reagan as to the realities of the world has begun,'' said one diplomat from a developing nation.
But the two-day economic summit was also a disappointment to some observers almost from the minute it ended, because the hundreds of millions of poor and hungry in the world will not be able, at this point at least, to see what is in it for them.
Participants argue in their defense that there are limits on what meetings of this kind can accomplish.
The participants did agree that the eradication of hunger in the world constitutes a ''first priority.'' But aside from dispatching new American agricultural teams and encouraging poor countries to attain self-sufficiency in the production of food, it is still not clear what concrete actions the Cancun participants will take to improve on their efforts to fight hunger.
With the means at hand to alleviate food shortages, widespread hunger and starvation remain a world scandal, and some participants acknowledged it as such.
As the conference co-chairmen, President Jose Lopez Portillo of Mexico and Prime Minister Pierre Elliot Trudeau of Canada put it, the long-term program proposed by Algeria to wipe out hunger by the year 2000 should be prepared. But will it? And even if it is prepared, will it mean only more words? Or will it mean action? they asked.
For President Reagan, meanwhile, the summit was, if nothing else, a public relations success. The President is widely regarded in developing nations as unsympathetic to third-world needs. But at Cancun he showed himself willing to listen. And by setting expectations for the summit fairly low before his arrival here, he made almost any ''give'' on his part look like a step forward.
Mr. Reagan's agreement to a statement advocating a renewal of global negotiations on third-world problems, while heavily hedged with conditions, seemed to give at least a few developing world leaders reason to hope the President might be more flexible on that issue than he had been.
Leaders of developing nations who have at times been acerbic in their criticism of the US, such as Algeria and India, seemed to give Mr. Reagan the benefit of the doubt at almost every turn. Some observers noted that Algeria has an interest in maintaining its US-supplied technology and its gas exports to the US. And India, meanwhile, is still awaiting approval of a multibillion dollar loan from the International Monetary Fund, in which the US wields significant influence.
But there was obviously more to the ''Let's be nice to Reagan'' attitude than that. It was almost as if some nations had been worn down by the Americans' resistance to global negotiations - which by implication mean a greater sharing of economic power - and are now willing to do the best they can to make the best economic deal possible with the US on a one-to-one basis.
American officials at the summit said that in their private talks with President Reagan, third-world leaders hardly even mentioned the global negotiations which were supposedly the central point of contention at the Cancun conference.
The US has been reluctant to enter such negotiations because they are to come under the auspices of the United Nations General Assembly, a forum where the US can easily be outvoted.
President Reagan was not the only one to describe himself as a ''learner'' at the summit. Britain's Prime Minister Margaret Thatcher told the British Broadcasting Corporation that a talk which she had with India's Prime Minister Indira Gandhi had brought home to her the seriousness of some of the poor countries' problems. It was not clear why she had failed to become equally aware of those problems during her official visit to India only a few months before.
President Reagan acted not only as a learner but also as a teacher during the conference session on food and agriculture. It was in this session that the President was most active, several times extolling the virtues of American farmers.
President Reagan repeatedly advocated the free market and private enterprise, but some delegates later complained that he neglected to stress the heavy role which government support played in the development of the American West.
''Look,'' said one third-world delegate, ''the Americans did not invent freedom 200 years ago.
''And to us, their kind of freedom looks like the freedom of the lion to swallow the gazelle, the freedom of the multinationals to roam the world at will.''
Mrs. Gandhi at one point gently rebuked President Reagan, according to a diplomat, by pointing out that progress in India's agriculture, which had reached self-sufficiency a few years ago, was derived in good part from government support in the form of land reform, agricultural credits, price supports, and irrigation, fertilizer, and pesticide services.
It was Mrs. Gandhi who perhaps best summed up the Cancun conference: ''The very fact that we could have a declaration is progress. When we came here, most of the world thought we would quarrel and disagree. . . . All you can hope for is bringing people slightly more together. Cancun has succeeded in that.''