Describing his achievements in his first year in office as modest - "at least we didn't sink" - Mexico's President Jose Lopez Portillo said he looked forward to two years hence, when he expects to see that a whole series of reforms will have been carried out.

In an interview at Los Pinos, the Mexican equivalent of the White House, President Lopez Portillo said the anticipated reforms will be based on the rapidly expanding surpluses of Mexico's oil wealth and the exploitation of other raw materials.

"The structure of injustice that has prevailed for centuries must be brought to an end." he said. "That is the basic challenge this country is facing."

He was in a confident mood and several times enlivened our talk with the dry humor and the quick smile that have helped to make him an increasingly popular figure in this one-party country.

"We must not let the oil go to our heads. During the next two years we must set up adequate projects for its use. The result must not be to make the rich richer and the poor poorer."

He used the expression "structure of injustice" two or three times, showing that he understands the scope of the enormous problems he faces: unemployment and underemployment of up to 40 percent of the work force, a population explosion with a 3.4 percent to 3.6 percent yearly increase, dire poverty alongside great wealth. Asked whether he considered himself to the political right, as some of his admirers have said. Lopez Portillo replied:

"I do not believe in the politics of geometry. I am neither of the right nor of the left. I was born in the Revolution. But the Revolution of Independence is not enough. That is not the solution in itself. Nor was the separation of church and state enough. These opened up the road for a solution."

He says he believes political direction depends not on political slogans but on the man behind the slogans. The confidence he has begun to inspire is evident in many ways. The capital that left the country in the two years preceding 1977 has started to flow back. This is true particularly of foreign capital, which had become alarmed by his predecessor Luis Echeverria's spending, both at home and abroad. Echeverria's spending had been considered excessive by foreign investors.

Under Lopez Portillo, Mexico's rate of inflation has dropped from 30 percent to 22 percent. The peso, which had been devalued under Echeverria and allowed to float, has held steady at 22 to the dollar.

Lopez Portillo claims to be undisturbed by the dispute with the United States over the price of natural gas to be sold north of the border. He says: "We are a patient people. We will stand behind our fence and hold up our sign that says $2.60 [per 1,000 cubic feet of gas]. We believe this will eventually prevail."

He has just had a visit from California's Gov. Edmund G. (Jerry) Brown Jr., whose aim was to generate interest in routing gas pipelines to the western, rather than eastern, half of the United States. With Brown cametransmission companies to discuss possible projects with Diaz Serrano, the director general of Petroleos Mexicanos, the government corporation with complete jurisdiction over oil and gas.

Lopez Portillo appointed Serrano, whom he has known since childhood, to that key post, and has said he believes Serrano to have every qualification to carry through a task of increasing magnitude. As a private contractor in drilling and exploration, Serrano had logged considerable experience in Texas.

Lopez Portillo is thoroughly familiar with the difficulties President Carter has had in achieving an extremely ambitious energy policy. His comment on this: "I do not believe in intervening in the affairs of another state just as I do not expect intervention in the affairs of my nation."

As to the relationship between the United States and Mexico, he says he believes that with the work of a series of commissions initiated a year ago, things are moving in a favorable direction. The basic need is to create jobs so that exports to the north will not be men, but goods. The problems between the two countries are wrapped in a single package, and the solution must not be piecemeal but instead must cover the spectrum.

Lopez Portillo says that while U.S. attitudes toward Mexico are sometimes objective, they too often reflect deeply ingrown prejudices. The stereotypes out of the past are difficult to overcome. The news out of Mexico more often than not fits stereotypes of poverty and violence.

Lopez Portillo sketched in brief his view of past and future. He has more reason, in my opinion, to be confident of better times ahead than has President Carter. And the reason for the upbeat outlook is not just oil. It is also the sure direction of a steady hand on the tiller.