MANILA, Philippines (AP) _ Troops opened fire on leftist workers Wednesday after a bomb exploded on a picket line, and suspected Communist rebels killed six people in the country's second-largest metropolitan center.

Three soldiers and three strikers were wounded in the picket line violence in Manila, police said.

The killings by suspected Communist rebels occurred Tuesday in Cebu City.

Meanwhile, police questioned two men about the assassination Sunday of a staunchly anti-Communist Cabinet member, Local Governments Secretary Jaime Ferrer.

Wednesday's shooting occurred about 7 a.m. at a meat-packing plant in suburban Manila after troops tried to break up a month-long strike by the May 1st Movement, the country's most militant union.

The military claims the union is infiltrated by Communists; the union denies the charge.

Police said a small bomb exploded, prompting troops to open fire. Workers interviewed by a private radio station denied there had been an explosion and said the troops had tried to push the strikers back toward a gate.

''Some of the soldiers fired into the air, and some at us,'' said Rogelio Bosco, one of the workers.

In Cebu City, 350 miles south of Manila, Police Col. Antonio Sable said two gunmen killed two officers in front of dozens of frightened children as the policemen directed traffic at a school.

The gunmen fled with two accomplices who stood guard during the attack. None of the children was hurt.

Hours later, four rebels killed a third traffic policemen in a Cebu suburb. After sundown, a Philippine Constabulary officer, a militiaman and a civilian were shot dead by rebels in a neighborhood near the center of the city.

In Manila, police questioned two men about the slaying of Ferrer and his driver, but neither was charged.

President Corazon Aquino told reporters on Tuesday that police had several theories about who killed Ferrer ''but no significant leads.'' She refused to elaborate or answer other questions.

Witnesses have told police three to five men riddled Ferrer's car with automatic weapons fire about a block from his home. No group has claimed responsibility, but speculation has centered on the Communist rebels.

About 50 police and soldiers have been murdered this year in the Manila area. Communist assassins are blamed for many of the deaths.

Former Defense Minister Juan Ponce Enrile, who served both ousted President Ferdinand E. Marcos and Marcos' successor, Mrs. Aquino, termed Ferrer's death unfortunate. He noted no Cabinet minister was killed while Marcos ran the country.

Enrile said Tuesday night he was concerned because of the way in which Ferrer died and because it came at a time when the government is trying to bring stability to the nation and improve the economy.

''The death of a high ranking Cabinet member is surely a source of apprehension, not only by our people but by the people of the world,'' Enrile said in a television interview. ''They will say 'What's going on in that country? The condition of law and order in that nation is such that even a Cabinet member is not safe any more.'

''I must say that the Marcos government ... (ran) the country for 20 years and none of its Cabinet ministers was ever dealt with in the manner Jimmy Ferrer was dealt with by the assasins,'' Enrile added. ''It's unfortunate for the nation. And I condole with the family.''

Asked who would benefit from the assassination, Enrile replied:

''There are a lot of people who will benefit ... political people who have been frustrated by his decisions; people who harbored ill will against him; ideologically motivated people who may wish to project the inability of the government.''

Enrile was Marcos' defense minister for 16 years but broke with him in February 1986 and helped lead the military revolt that ultimately forced Marcos to flee to Hawaii. Mrs. Aquino retained Enrile as defense minister but fired him last November after a coup attempt by his followers.