MEXICO CITY -- Ernesto Zedillo became president of Mexico on Thursday, promising profound political and legal reforms to match the opening of the market that resulted last year in a free trade agreement with the United States and Canada.


The U.S.-trained economist caps an unlikely journey when he assumes the red, green and white presidential sash to start a six-year term as leader of this country of 90 million.


Zedillo, a former shoeshine boy, achieved a Yale University doctorate in economics. Bypassed once for his party's presidential nomination, he was thrust into the campaign by the March assassination of Luis Donaldo Colosio, first choice of the ruling Institutional Revolutionary Party, or PRI.


He won the presidency Aug. 21 in Mexico's most credible elections ever.


Zedillo, 42, has pledged to use the near-absolute powers of Mexico's presidency to weaken his own office.


He says he will give greater independence to the congress, the courts and local governments as well as to the PRI itself. He has also pledged to end the practice of having the president handpick all top PRI candidates.


Zedillo, former budget and planning minister under President Carlos Salinas de Gortari, is sure to continue his predecessor's freemarket economic policies -- a commitment underlined by the cabinet choices announced Wednesday.


Leading negotiators of the North American Free Trade Agreement were named heads of treasury, trade and foreign policy. Seven other freemarket economists also were appointed to the 25-person cabinet.


Zedillo also made a political opening by naming an opposition party member to the cabinet for the first time. Antonio Lozano, a conservative, will be attorney general -- a crucial post since Zedillo has made fighting government corruption a major part of his campaign.


On Tuesday, Zedillo reached out to the left as well, meeting with leaders of the Democratic Revolution Party and promising reforms to help make Mexico more democratic. Salinas never met publicly with leaders of the main leftist opposition during his administration.