MANILA, JULY 3 -- President Corazon Aquino said today that Imelda Marcos would remain barred from this country on grounds of "national interest and security" in spite of her acquittal Monday by a New York jury of charges of having looted the Philippine treasury.

After a cabinet meeting lasting more than three hours, Aquino declared, "The return of Mrs. Marcos would enable her to mobilize the underground network of the Marcos dictatorship, which is designed to overthrow this government and endanger our democratic gains and economic momentum."

Without offering any specific evidence, Aquino said Marcos "encouraged and supported" a coup attempt last December by thousands of soldiers led by supporters of her husband, the late ex-president Ferdinand Marcos.

Several other leading politicians here said, however, that in light of the New York verdict, it may be time to lift the travel ban and allow Marcos to come home to face criminal trial.

Senate President Jovito Salonga said that allowing Marcos to come back would be a good test of the country's newly reformed legal system, while House Speaker Ramon Mitra said Marcos should return since "it is here in our country where she should have been tried in the first place."

According to Filipino and foreign analysts, the acquittal has raised new fears of instability and dealt another setback to Aquino's efforts to usher in a period of political normalcy.

The verdict was greeted with surprise and dismay by government officials. Opposition politicians hailed the ruling as "a slap in the face for the Cory administration," in the words of former assembly member Homobono Adaza.

Speculation arose over what role Marcos -- the once-powerful first lady -- might take here.

"She can be a player, with all that money, and with northern Luzon still sympathetic to the Marcoses," said newspaper columnist Teodoro Benigno, a former spokesman for Aquino. "Politics is in a state of flux. She has a name, she has allies . . . and she has some sympathy because of her acquittal."

Some analysts here predicted a possible surge in political violence, and further military unrest. "I don't know what her motives are," said a Western diplomat, "but if Imelda is revenge-minded, she can now use some of her illegal loot to fund right-wing activity here."

Marcos's acquittal also has seriously complicated the Aquino government's efforts to pursue its own legal cases against Marcos, who is accused, with her late husband, of looting some $10 billion from the treasury and salting much of it in Swiss bank accounts and in real estate.

{A Swiss official quoted by the Associated Press in Bern said the acquittal in New York would not impede official Philippine efforts to recover assets purportedly hidden there. In Washington, Reuter quoted a U.S. official as saying the U.S. government was unlikely to lift an order forbidding Marcos's departure, issued because of her "potential for destabilizing activity" in the Philippines.}

Marcos now has 33 corruption cases pending against her here. But the government has been reluctant to charge her criminally, since that would entail allowing her to return to this country to defend herself.

Close associates here of Marcos said her next legal step will be to petition the Philippine Supreme Court to reconsider its October 1989 ruling that upheld the travel ban. The court ruled 8 to 7 that the government could keep Marcos out on national security grounds, but her supporters now say that because of the New York verdict, the pro-Aquino majority on the court may be shaky.

Aquino has already suffered one embarrassing defeat before the Supreme Court: it ruled overwhelmingly last month to throw out rebellion and murder charges against opposition Sen. Juan Ponce Enrile and 22 others who were accused of participating in last December's bloody coup attempt. A majority of the justices may now rule in favor of a return by Marcos, according to Rafael Recto, a family lawyer who also is accused of participating in the coup attempt.

Recto said it was "baloney" for the government to ban Marcos because of the supposed threat to security. "If this government is unstable, it is not because of Mrs. Marcos," he said. "They brought it on themselves." He added that Marcos wanted to return for a proper burial of her late husband and to clear her name in the courts, but not to become actively involved in politics.

"She will not become active in politics, that I can assure you," said Recto.

Still, others here said that Marcos is likely to make a fresh bid to play a key role behind the scenes in picking a successor to Aquino, who has repeatedly pledged not to run for reelection when her six-year term expires in 1992.

"I don't think Imelda will run for president herself -- but it's not improbable for her to become one of the kingmakers," said Adaza, who also has been accused of being one of the coup plotters.

A Western diplomat said he did not rule out the possibility that Marcos might try to run for president herself, if she could sneak back as did a business associate of her husband, Eduardo "Danding" Cojuangco. He flew in undetected last November in defiance of an identical government travel ban.

"She probably sees herself as presidential material, even if nobody else does," this diplomat said.