A commission appointed by Philippine President Corazon Aquino convened today to start writing a new constitution amid attacks from the political right and left.

"Please be quick," Aquino told the 48-member body, called the Constitutional Commission, in a speech at its opening session. She urged the commission to complete a new charter within three months to pave the way for elections of national legislators, provincial governors, mayors and other local officials.

The convening of the commission in the session hall of the Philippine legislature, which Aquino abolished in March, came a few hours after police used tear gas and water cannons to break up a vigil at the meeting site by about 1,000 protesters supporting deposed president Ferdinand Marcos. Several thousand supporters of Marcos completed a march to Manila yesterday from Marcos' home province of Ilocos Norte after several stone-throwing clashes with Aquino's supporters.

In recent days the commission also has been condemned by Jose Maria Sison, the founding chairman of the Communist Party of the Philippines, who was released from prison by Aquino soon after she took office Feb. 25.

Sison predicted that the commission would do nothing to remove the U.S. bases or the "ceaseless stranglehold" of American multinational firms. The commission "is practically in the pocket of the U.S.," he said.

Aquino proclaimed a provisional revolutionary government March 25 and announced a temporary "freedom constitution," giving her broad powers to govern by decree and dismantle the "Marcos dictatorship" erected by her predecessor during his 20-year rule. She also unveiled plans to fill a new constitution-drafting body through appointments rather than elections.

On May 25, she appointed 44 members to the commission and allotted five seats to the "opposition," consisting of supporters of Marcos' government, and one to an indigenous Christian sect that strongly backed Marcos. The sect member and one opposition member subsequently declined to participate.

Aquino said to commissioners today, "Please limit yourselves to your constitutional mission," refrain from usurping the future legislature's work and "not be distracted by political debate and matters of policy."

Commissioners said afterward she may have been referring to contentious issues, such as regional autonomy, land reform and the presence of two U.S. military bases, that might delay the deliberations.

A youth representative on the commission, University of the Philippines student council president Jose Gascon, 22, has said publicly that he would work for the abrogation of a mutual defense pact with the United States to ensure the removal of the bases when the current agreement expires in 1991.

Former Supreme Court justice Cecilia Munoz-Palma, who was elected president of the commission today, said issue of the bases should be avoided, along with education, family rights and foreign policy. She said the main concerns of the body ought to be deciding what form of government to have after the muddle of Marcos' 1973 constitution, which combined a presidential and a parliamentary system.

Blas Ople, a labor minister under Marcos and now the leader of the opposition faction on the commission, said Aquino's admonition was "reasonable advice." He said one potentially murky issue is regional autonomy, or decentralization, with a variety of cultural minorities seeking to have their rights specifically mentioned in the new constitution.

However, Ople said the commission could be overshadowed by a need to address the "highly political" status of Aquino and her vice president, Salvador Laurel, in the constitution through a "transitory provision" fixing their term of office following the popular revolt that installed them. He said a plebiscite on the constitution thus could turn into a referendum on Aquino and Laurel, and he held out the possibility that he and other opposition members might end up working against ratification.

Sison has said the commission has eight members who strongly support "the basic interests of the toiling masses." He urged them to walk out once a "final counterrevolutionary sense and shape of the constitutional draft becomes clear."