A citizens' poll-watching group today charged that at least 3.3 million Filipinos were unable to cast ballots in this month's presidential election because of "massive disenfranchisement of voters" by the government of President Ferdinand Marcos.

The group, the National Citizens' Movement for Free Elections, known as Namfrel, also released data for the first time indicating that a vote count by the Marcos-controlled National Assembly was based on fraudulent election return documents from throughout the nation. The assembly declared Marcos the winner early Sunday after opposition legislators walked out to protest the canvassing of "spurious" returns.

Namfrel and a government group counted returns using the same raw data as the assembly, but the assembly's tally is the only official one.

Thousands of youths protested at the U.S. Embassy and state-run television building against Marcos' disputed election victory. The demonstrations came as U.S. special envoy Philip C. Habib met separately today with Prime Minister Cesar Virata and Labor Minister Blas Ople, and the peso fell to a record low of 22.043 to the dollar.

Namfrel's data has been turned over to a U.S. observer group sent here last week by the White House to continue the election monitoring work of a team led by Sen. Richard Lugar (R-Ind.) and Rep. John Murtha (D-Pa.). The observer group, headed by Allan Weinstein, president of the Boston-based Center for Democracy, met with Marcos today for 2 1/2 hours and received documents and photographs that Marcos said prove his claims that the opposition was to blame for most of the election fraud and violence.

The release by Namfrel came as the Marcos government, under intense criticism by opponents over charges of political violence, announced that Arturo Pacificador, a staunch political ally of Marcos who serves as assistant majority floor leader in the assembly, was charged with three counts of murder today in connection with the ambush killings two years ago of seven opposition supporters in his home province of Antique.

Those killed in the ambush on the eve of parliamentary elections in May 1984 were supporters of his opponent, Evelio Javier, who himself was gunned down Feb. 11 in the Antique provincial capital of San Jose after having served as a local campaign manager for Aquino in this month's election. The governor of the province has charged that the gunmen used vehicles belonging to Pacificador.

Pacificador has denied involvement in the 1984 killings and Javier's murder. He has not been charged in the Javier case. Prosecutors in Antique recommended murder charges against Pacificador in the ambush case in 1984. There was no explanation of why the charges were filed today.

According to Namfrel president Jose Concepcion, "massive disenfranchisement of voters," mainly in opposition areas, contributed substantially toward changing the "margin, if not the outcome, of the election." He said the assembly's figures showed that only 77 percent of registered voters actually cast their ballots on Feb. 7 (voting is compulsory in the Philippines) compared with 89 percent in 1984, when there was a strong and well-organized boycott.

Based on the turnout figures, he estimated that 3.3 million people were unable to vote for various reasons. Previous estimates had ranged as high as 2 million.

Concepcion reported "an emerging pattern of disenfranchisement" in which the 10 cities and provinces with the highest percentages of actual votes to registered voters were all won by Marcos. Of the 10 cities and provinces nationwide with the lowest turnout percentages, eight were won by Aquino. Among them was Ifugao Province, in northeast Luzon, where only 22 percent of registered voters cast ballots compared with 93 percent in 1984.

Marcos has denied that his party was responsible for disenfranchisement, insisting that the problem also heavily affected his supporters.

Concepcion also disclosed figures showing that Aquino had lost tens of thousands of votes in the assembly's official canvassing.

Final assembly totals showed fewer votes for Aquino in many areas than partial returns assembled by Namfrel. For example, Concepcion said, on the southern island of Basilan, Namfrel had Aquino leading with 22,743 votes to Marcos' 15,182 with 69 percent of precincts reporting. But the assembly in its final tally put Marcos on top with 22,387 votes to 3,005 for Aquino.

In the central Philippines province of Leyte, the home of Marcos' wife, Imelda, Aquino had 170,978 votes with all precincts reporting in Namfrel's count, but 143,261 votes in the legislature's final tally. In the province of Isabela, part of Marcos' "solid north" base of support, Aquino had 26,443 votes with 19 percent of precincts reporting in Namfrel's count, and 20,072 in the assembly's final count.