Miguel de la Madrid Hurtado, Mexico's planning and budget minister was named 1982 presidential candidate of the ruling political party today, virtually ensuring that he will be the nation's next president.

De la Madrid, 46, will be the candidate of the Institutional Revolutionary Party in the elections next July.

Since the party, which is equivalent to the political establishment, has won every presidential election since 1929, de la Madrid is expected to replace Jose Lopez Portillo for a single, six-year term on Dec. 1, 1982.

Like the incumbent president -- who by tradition is authorized to handpick his own successor -- de la Madrid has had a long career in public administration but has never held an elected post. A lawyer by training, he holds a master's degree in public administration from Harvard University and is generally regarded as a politically middle-of-the-road technocrat and an expert in fiscal affairs identified with state-led economic growth.

Although Lopez Portillo last week announced that the official candidate would be disclosed soon, the naming of his successor nonetheless came earlier than expected.

It was widely assumed that Lopez Portillo would postpone the event until after he has served as host for the North-South summit here next month to avoid a status as lame-duck president.

Mexico's succession ritual began as the three main sectors of the ruling party announced that they would back de la Madrid's candidacy, which they will officially endorse in a party convention next week.

Although Mexico has the formal makeup of a democracy, it essentially is run by one party, which embraces the country's main political forces, including the private sector, the military, the bureaucracy, the unions and the intellectuals. While there is no opposition party of national importance, several, including the Communist Party, are expected to run candidates.

Rather than having to compete with political opponents, de la Madrid's six-month political campaign will be designed to make him known to the public and to expose him to grass-roots problems around the country.

Of the three front-runners in the official party, de la Madrid has been the favorite of the business and banking community. This was reflected on the stock exchange this morning which jumped 10 points as the news broke but was closed after the first hour of trading.

Born in the tiny western state of Colima on Dec. 12, 1934, de la Madrid is a descendant of Spanish immigrants and, unlike the majority of Mexican politicians who are of mixed Spanish and Indian blood, he looks distinctly European.

De la Madrid speaks fluent English and is said to have a more open-minded attitude toward the United States than most members of the deeply nationalistic political establishment.

In a private conversation he once said that Mexico would be well served to "have a better understanding" of American society and politics.

Like his friend Lopez Portillo, who likes to describe Mexico as "not underdeveloped but underadministrated," de la Madrid is part of a group of technocrats who believe Mexico's government urgently needs to be modernized and oriented more toward management than the traditional populism.

Many political analysts feel that de la Madrid's candidacy is likely to be a continuation of Lopez Portillo's emphasis on public administration and his growth-oriented policies at home.

The new candidate, who is well-to-do but not extremely rich by Mexican standards, is married and has five children.