MEXICO'S dominant party, nominating the budget minister to be president, signals its intention to stick with the policies of economic restraint. As a leading figure in a program of austerity, Carlos Salinas de Gortari was not the most popular of the leading candidates for the nomination. But the choice isn't as implausible as it might seem at first glance, for those policies are now beginning to pay off for Mexico. The capital flight that has weakened Mexico severely over the past decade has now reversed itself. Since the beginning of the year, several billion dollars have come into Mexico from abroad, the most sincere kind of a vote of confidence in the future of the country. That kind of inflow represents the best and most productive way for Mexico, or any of the indebted Latin countries, to reduce its burden.

But if Mr. Salinas is supported by business and the people who manage money, he is regarded with deep suspicion by much of the labor movement, and his candidacy may prove divisive. His Institutional Revolutionary Party (PRI) has, for 57 years, embraced both business and labor with such skill, and with such lavish use of patronage, that its nominees have always won the presidency -- and there's a very strong presumption that Mr. Salinas will win the 1988 election for which the campaign now begins. But the crises of the Mexican economy in the 1980s -- first its inability in 1982 to meet the payments on its soaring debts, then the collapse of oil prices last year -- have raised tensions and begun to generate a new kind of politics there.

Over the past several years, for the first time since it took hold of Mexican politics, the PRI has faced a vigorous opposition, the right-wing National Action Party (PAN). Perhaps that's another reason why the PRI chose Mr. Salinas. PAN reflects a rebellion against the tradition of closed markets and paternalism that is new to Mexico. Mr. Salinas' ideas often run in the same direction, and perhaps the leaders of the PRI are trying to draw some of the rebels back into their party.

Mexico has not yet found its way back to economic balance. Its inflation rate is running well over 100 percent a year. Wages have dropped severely over the past five years. Its oil fields have proved a source of enormous yet utterly unstable wealth. But under its present president, Miguel de la Madrid, most of its leaders seems to believe with increasing confidence that they are moving back toward solid growth. By nominating Mr. Salinas, his party is moving to preserve the progress already made, and to maintain it through another six years.