MANILA, Philippines--Thirty computer operators marched out of the government's election commission yesterday, claiming the ballot counting that showed President Ferdinand E. Marcos defeating Corazon Aquino was falsified.

An international observer group, meanwhile, accused Marcos' partisans yesterday of vote-buying, intimidation, snatching ballot boxes and tampering with election returns in Friday's special presidential election.

The computer operators wept on each others' shoulders after parading single file out of the Marcos-appointed commission's counting center.

"There was something wrong," a woman operator explained. "What's posted on the tabulation board does not tally with the computer board, and we don't know who is doing it. We can't take it any more."

The woman, who refused to give her name, told The Associated Press that workers spotted the problem Saturday night, when Mrs. Aquino was leading in the commission's count by 100,000 votes. By midday yesterday, Marcos had taken over the lead.

By this morning, with 28 percent of the precincts reporting, the commission's unofficial tally gave Marcos 3,056,236 votes to Mrs. Aquino's 2,903,348, a split of 51.28 percent to 48.72 percent.

But an independent count by the National Movement for Free Elections, a citizens' ballot-monitoring group known as NAMFREL, had Mrs. Aquino in the lead by 5,576,31953.7 percent to 46.3 percent.

The NAMFREL tally represented 49.14 percent of the Philippines' 86,036 precincts. Final election results from this nation of 7,100 islands are not expected for days.

Marcos' latest six-year term was due to expire in 1987, but he called the special election to show domestic and foreign critics, particularly in the United States, that he still enjoyed overwhelming support in the Philippines.

Certification of the election result is up to the National Assembly, which was due to begin its own separate canvass today.

Citing the difference between the two counts, Political Affairs Minister Leonardo Perez said he would seek the assembly's approval to terminate all other vote-counting immediately.

Sen. Richard Lugar, R-Ind., co-leader of a 20-member U.S. delegation observing the elections, said the election is "teetering on the brink of disaster but still in place."

Speaking on ABC's "This Week With David Brinkley" in an interview from Manila, Lugar added: "No one has any idea who's ahead."

An international observer group, composed of 44 pollwatchers from 19 nations, said delays in the count were "damaging to the credibility of the process."

The statement, read by former President Misael Pastrana of Colombia, read: "We saw many instances of vote-buying, attempts at intimidation, snatching of ballot boxes and tampered election returns." It said many voters, particularly in Manila, where Mrs. Aquino was heavily favored, found their names were not on registration lists.