Opposition leaders Thursday insisted the governing party stole the presidency, which final results gave to Carlos Salinas de Gortari by the slimmest margin in the Institutional Revolutionary Party's history.

The opposition won four seats in the 64-seat Senate, the Federal Election Commission said late Wednesday, releasing a week after the balloting vote totals it originally promised for election night.The centrist governing party, known as the PRI, had not lost a presidential, gubernatorial or Senate race in its 59 years.

It was not yet known whether the PRI lost the two-thirds majority required for approval of constitutional reforms in the Chamber of Deputies, the lower house of Congress.

The PRI-dominated election commission said Salinas received 9.64 million votes, or 50.36 percent, far below the 70 percent the PRI has traditionally won.

Cuauhtemoc Cardenas of the leftist National Democratic Front was second with 5.96 million, or 31.12 percent; and Manuel J. Clouthier of the conservative National Action Party was third with 3.27 million votes or 17.07 percent. Two minor candidates accounted for the rest of the vote.

Of 38 million registered voters, 50.3 percent cast ballots, the commission said. Government and party officials initially described the turnout as larger than the 75 percent in 1982.

High turnout was one of the reasons they gave for the delay in releasing results so the low turnout gave rise to two theories: The 1982 turnout was inflated - or opposition votes were not counted this time.

Opposition representatives on the commission accused it of fraud and said the release of the vote totals was delayed so they could be doctored.

"It appears that there are two Mexicos," said Jorge Amador, a National Democratic Front supporter on the commission.

He said there is a modern Mexico where the federal electoral code is respected, honest results were posted and the victorious candidate is Cardenas, and a second, backward Mexico "in which the federal electoral code is not known, is not applied," and the the popular will was thwarted.

"In many garbage dumps and on isolated roads, in some rivers of the republic are flowing electoral material marked in favor of parties of the opposition," he said early Thursday.

Amador's aides carried into the commission boxes of ballots, some of them partially burned and others he said they found in the streets.

He said the vote should be annulled in 10,000 of the more than 54,000 polling places because opposition representatives were denied access or ejected illegally.

Diego Fernandez de Ceballos of the National Action Party said: "We do not accept this election as clean because there were violations of the law," because the (state) governors pressured voters, because the resources of the political power were at the service of the PRI, because the official and private television was for the PRI.