QUITO, Ecuador (AP) _ With results in from 19 of 21 provinces, centrist Quito Mayor Jamil Mahuad today appeared headed for victory over a banana tycoon in Ecuador's presidential runoff.

Elections officials gave Mahuad, who has a master's degree in public administration from Harvard University, a preliminary 7.6 percent lead in Sunday's vote over his populist rival, Alvaro Noboa.

But with results still not in from Noboa's coastal stronghold of Guayas, Ecuador's most populous province, the margin was expected to shrink.

The final result, which had been expected today, will likely be delayed until Thursday, election officials said this afternoon.

``I don't think the results will be released today because we still do not have all the votes from Guayas,'' election tribunal Vice President Eduardo Villaquiran said.

Mahuad already has claimed victory, meeting with officials to discuss the makeup of his Cabinet. But Noboa has refused to concede defeat, saying that his private exit poll showed him winning narrowly.

He charged the Mahuad camp with organizing a fraud.

About 100 Noboa supporters surrounded the elections office in the port city of Guayaquil, Noboa's home town, after he called on them to go to there protect his votes.

``They have forced us to militarize vote-counting centers to protect the people working there,'' said Patricio Vivanco, president of the electoral tribunal.

Foreign observers who monitored the vote have rejected fraud charges.

Mahuad, 48, and Noboa, 47, were the top vote getters in the first round of voting on May 31. Since neither won an outright majority, a runoff was called.

The winner will take over an Andean nation of 12 million people with its democracy and economy in tatters. The economy is expected to grow by up to 1 percent in 1998, battered by El Nino-driven floods and mudslides and falling prices for its main export, oil.

The new president must also repair Ecuador's 19-year-old democracy, which almost collapsed in February 1997, when Congress removed eccentric President Abdala Bucaram from power for ``mental incapacity'' amid massive street protests and a paralyzing national strike.

Congress named Fabian Alarcon as interim president, but for 48 chaotic hours following Bucaram's ouster, three people simultaneously claimed to be president.

Mahuad had earned a reputation as a clean, effective politician during his six-year stint as Quito's mayor. He had the support of Ecuador's political elite and business community.

Noboa, Ecuador's richest man, had campaigned as the candidate of the poor, despite his wealth, and had the support of disgraced former President Bucaram's Roldosista party.

The winner will replace Alarcon on Aug. 10.