MANILA, Philippines (AP) _ Vice President Joseph Estrada, the main opposition candidate, retained a strong lead today in the Philippine presidential count despite escalating criticism over the slow pace of vote-tallying.

Counting of senatorial races, due to start in Manila today, was delayed for at least a day after no provincial tally sheets arrived.

Estrada's party claims that government officials have been pressuring their local counterparts to slow the count from Monday's election to enable cheating by the ruling party.

``There seems to be an attempt to thwart the will of the electorate,'' said Sen. Orly Mercado, spokesman for Estrada's party.

Estrada said election returns have been delayed in 19 of the Philippines' 78 provinces.

The leading poll watchdog group, the National Citizen's Movement for Free Elections, said it may have to extend its original 10-day counting schedule while stepping up efforts to prevent possible fraud. It did not say how long they now expect to take.

The group's secretary-general aknowledged growing apprehension about the pace. ``The public has a right to be concerned when the count is slow,'' said Luz Guillermo.

President Fidel Ramos said he instructed the government election commission to speed up the count and look into reports that some copies of tally sheets have not been provided to the watchdog group.

In the southern province of Sulu, election officials ordered ballots to be taken to Manila for a complete recount because of reports of irregularities and equipment breakdowns.

Hundreds of soldiers backed by armored personnel carriers escorted the ballot boxes to Manila.

With about 24 percent of the ballots counted in the 10-candidate race, Estrada continued to have a large lead with 37 percent of the vote, the poll watchdog group said.

Ramos' hand-picked candidate, House Speaker Jose de Venecia, moved into second place with about 13 percent. Senator Raul Roco dropped to third, slightly behind de Venecia, the group said. A majority is not needed for victory.

On Wednesday, Manila's influential archbishop, Jaime Cardinal Sin, called on Estrada's rivals to concede defeat.

Sin, who earlier warned that an Estrada presidency would be ``most probably disastrous'' for the country, issued a pastoral statement saying, ``I believe the trend is now clear.''

Estrada, a college dropout who has admitted a history of womanizing, heavy drinking and gambling, has been opposed by many in the country's traditional establishment, including Sin, Ramos and former President Corazon Aquino.