Charito Planas, former Philippine political prisoner and prominent activist-in-exile, is smiling as she remembers the last time, in 1978, that she heard the sounds of protest in her homeland. "Those who believe in the cause of democracy and freedom," she says, "were urged to make noise on the eve of the April 6 elections for five minutes.

"I remember the sister of Ninoy Benigno Aquino, the opposition leader who was assassinated Sunday said to me, 'Charito, where are we going to send the foreign correspondents for this noise demonstration?' And I said to send them to the usual crowded areas in Manila." It didn't matter. "Manila was literally shaken with pot-banging noise from 9 o'clock in the evening until the wee hours of the morning.

"And then the next day not a word mentioned in the paper, not a picture shown on TV nor mentioned over the radio about the noise demonstration that had taken place."

It was, Planas says, an example of the power of Philippine President Ferdinand Marcos to undermine the electoral rebellion she helped organize. The next day, the police moved to arrest Planas, forcing her into hiding. A few weeks later she left the country and started a new life as a rebel-in-exile fighting to end Marcos' rule.

Of an estimated 1 million Filipinos living in the United States, Planas is one of a small community of political dissidents. But the sounds of their dissent have grown louder since the assassination of Aquino. The exiled opposition leader was returning to the Philippines to lead the movement for the 1984 elections. Aquino, shot by an unidentified assailant moments after leaving his plane at the Manila airport, was in the custody of government security agents at the time. Most in the opposition believe Marcos plotted the assassination and are redoubling their efforts to try to oust him.

"I have a mission to inform the people in the United States of the situation, that the struggle that is taking place in the Philippines is not a contest between the United States and Russia," says Planas, her voice suddenly becoming more firm. "It is a struggle for economic justice.

"I describe the situation in the Philippines as being like a house full of termites--you can't simply replace the roof. You have to destroy the house and build a new one but you cannot do it by prayers, demonstrations and elections." What needs to take place, she adds, is a "people's revolution."

If there is a modern image of a rebel--green fatigues, scrawny body and haggard face--then Charito Planas shatters it. She is short, plump, lives in McLean and is 53 years old. But Planas is a rebel--she travels during most of the year to high schools, colleges and churches to talk of her life in Marcos' prisons, of her frustrating attempts to win elections that the government is believed to have manipulated.

Still, in the divided exile community here, Planas is subject to criticism for her foggy politics. A member of the exiled moderate opposition said, "I don't think Planas has a firm stand on anything." The woman, who requested that her name not be used, added, "I think she's an opportunist. She likes the limelight."

Planas was jailed for 14 months by Marcos after martial law was declared in 1972. Subsequently, she mounted a vigorous campaign in the parliamentary elections against the U.S.-backed government. The day of the 1978 assembly elections--in which Planas officially gained nearly one-third of the 3.1 million ballots cast--police raided her home and charged her with subversion. "Trumped-up charges," Planas now calls them, but they were sufficiently grave to force her to flee. "They say I won the election and lost the vote count," she chuckles.

The results of the election, won by a pro-Marcos slate headed by the president's wife, Imelda Marcos, were widely criticized as being entirely manipulated by the government. But Planas, one of the few women running on the opposition slate, was seen as the alternative to the policies and personality that Imelda Marcos represented. "Charito was given the role of confronting Imelda," said a Philippine activist here. "If a man had said some of the things she said, it would have been considered impolitic."

"If there had been a real election, we would have won," Planas now says, looking out of the windows of the Washington office where she is being interviewed. "That's why Marcos had to resort to fraud, intimidation and harassment in order to win."

Planas' political career began in Manila's 1971 mayoral election, when she challenged the incumbent and another pro-Ferdinand Marcos candidate. She lost, but gladly recalls the differences between herself and her opponents. "I went around with my secretary, also a woman, while my male opponents had armed bodyguards."

She rocketed to the forefront of the 1978 campaign for the interim National Assembly, which was led by Aquino. "Planas is a very colorful and gutsy woman," said a seasoned American observer of Philippine politics. Even one of her rivals in the moderate camp here admitted that Planas "can give speeches that excite people . . . She has a following in the Philippines."

In that country, where martial law was lifted two years ago--but where its authoritarian traces unquestionably remain--Planas was an anomaly in the ranks of rebels and in the society's upper class, from which she comes.

"My parents brought us up to have principles and fight for them, and to be charitable," she explains. "I started by being charitable, but I discovered that charity is not the solution to a problem that is widespread." A Catholic, Planas questions "how we can call ourselves children of God when so few have so much and so many have so little . . . We must share the fruits of the earth."

"Those who have the power and the wealth will not share," she says. "You are forced to use force."

But she has opposed the liberal, reform-minded strategies proposed by such moderates as Aquino, who came from the same kind of middle- to upper-class background. "We were friends in the sense that we were fighting a common enemy. But we had political differences," Planas explains.

She now calls for the moderates to unite with the left to form a front against Ferdinand Marcos.

At the same time, she distances herself from the tactics of violence advocated by Communist-led insurgents. "I don't think I could hold a gun and kill," she said. "I would not be able to shoot somebody."

She refuses to call herself a leftist. "I am not comfortable with labels . . . When you are labeled 'left' you are considered a Communist," she says, clearly troubled by the corner she is jammed into and at a loss to escape it easily. The leftist opposition, grouped under a coalition known as the National Democratic Front, includes a large Communist following. In fact, the front's military wing, the New People's Army, is Communist-led.

"I am not uncomfortable with the Communists," she offers. "I would not question their sincerity. They are working for the same goal."

President Reagan is scheduled to visit the Philippines later this year, and Planas is joining other Philippine activists and their congressional allies in a bid to have that visit postponed or canceled. Yet the seasoned dissident realizes the battles here and in the Philippines are not likely to become any easier after Aquino's slaying.

Ferdinand Marcos "is confident that even the killing of Aquino will not change the U.S. support for him," Planas says. But she insists the leftists are not anti-American.

"We distinguish between the American people and the government. The policy-makers have not learned from past mistakes. They have always supported dictators or repressive regimes whenever there is a struggle for economic justice. The dictators always fall, and when they fall," Planas believes, "the U.S. government falls, too."