MANILA, Philippines (AP) _ Officials today widened a probe into alleged vote-rigging in favor of the president's Senate candidates, and Imelda Marcos was sworn in as congresswoman in defiance of the electoral commission.

Officials said up to 30,000 votes were apparently added to the totals of three candidates aligned with President Fidel Ramos in the Marcos family stronghold of northern Luzon Island. Those gaining votes were former Justice Secretary Franklin Drilon, former House Speaker Ramon Mitra and former Rep. Juan Ponce Enrile.

Provincial officials were summoned to Manila to explain discrepancies in the vote count following the May 8 election.

``This was the worst case I have seen since I joined the commission five years ago,'' said commissioner Regalado Maambong, saying he thought there was intentional fraud.

The opposition National Peoples Coalition said it would challenge the count in 17 of the country's 76 provinces, which account for about 25 percent of the registered voters. Electoral commission chairman Resurreccion Borra said the investigation would extend to the other areas as well.

Ramos spokesman Honesto Isleta denied the administration was involved and said ``the president would not tolerate it.''

A week after the election, the unofficial count by the National Movement for Free Elections _ NAMFREL _ showed Ramos' candidates leading for nine of the 12 contested Senate seats based on reports from 62 percent of the precincts.

NAMFREL's figures apparently included the padded votes in Ilocos Norte province, where returns were retabulated today.

As of this afternoon, the official tabulations showed Ramos' candidates leading for eight seats. That count, however, was based on returns from only 21 provinces. It did not include votes from densely populated areas of central Luzon, metropolitan Manila and Cebu, where Ramos' coalition was strong.

Ferdinand ``Bongbong'' Marcos Jr., son of the deposed president, was No. 16 in the NAMFREL count but No. 7 in the official count.

Ramos has called the strong showing a ``fresh mandate'' for his administration. Despite 40 killings, Ramos described the elections as ``clean and orderly'' and said the outcome showed the country was on the road to stable, honest government after nearly 25 years of rampant corruption and social and political unrest.

In Tacloban, 350 miles southeast of Manila, Mrs. Marcos took her oath Sunday as a member of the House of Representatives after election officials acknowledged she won 70,471 votes to 36,833 for her closest rival.

``It is clear I am the peoples' choice,'' she told reporters today.

Officials refused to certify her as the winner because the electoral commission said she failed to meet residency requirements to run in the district. The ruling has been appealed.

Mrs. Marcos said that with her victory, ``the world realized that they were deceived nine years ago.'' She was referring to the February 1986 uprising that toppled her husband, President Ferdinand Marcos, and propelled Corazon Aquino into the presidency.

Marcos died in exile in Hawaii in 1989, and his family returned in 1991.