After much ado about terrorism, the State Department at last consented to allow leftist Italian playwright Dario Fo to visit this country, and so it was that he took the stage at the Belasco Theater, where one of his plays is being produced, and took pains to thank the fellow who was making him such a cause ce'le bre -- the president.

"The star publicist," said Fo, a perpetually amused fellow, speaking through a translator, "has been Ronald Reagan himself, and he has done it with such intelligence that only a politician as he can do. In fact, he personally phoned me in Italy. He said, 'I won't give you permission right away, and that will begin the interest. Then I'll refuse the visas a couple of times. Then we'll do the big, big surprise -- I'll give you the visa.' "

He glanced around the theater, filled with press.

"Before this great publicity drive, I wasn't known by many in the United States," said the 58-year-old writer and actor. "Today even the candidate defeated by Reagan knows Fo."

Maybe yes, maybe no.

Civil liberties activists and members of the theatrical community have, for some time, been aware of Fo. He and his wife, actress Franca Rame, are well known in Italy both for their support of left-wing causes and for their troupe, which often performs in the street. The Italian government, the pair say, has protested every single one of their productions ("For which we are grateful," deadpans Fo), and the Fos go out of their way to respond in kind -- an Italian politician who opposed abortion soon found himself portrayed in a Fo production, pregnant. The couple has also enjoyed success outside Italy. "Accidental Death of an Anarchist," the political farce that opened here this week, has been staged in more than 100 productions around the world.

Because of their activism, however, the Fos have twice been forbidden permission to visit this country -- in 1980, when they were scheduled to perform in an American tour, and again last fall, when they were to perform at the New York Shakespeare Festival. ("An Evening Without Dario Fo" was the billing for an actors' protest that followed.) The explanation, from a State Department spokesman, was a section of the McCarren-Walter Act, which bars "aliens who are members of or support anarchist, Communist or terrorist organizations."

Franca Rame, who, like her husband, speaks no English, says, quite openly, that she was in her youth a member of the Communist Party. Both she and her husband deny any sympathy for terrorism, however, and in the matter of personal politics identify themselves rather as leftist independents.

"Democratic progressives," says Fo. "Of course we are from the left, but we are not joining a political party."

A twinkle that transcends language barriers.

"We are free dogs," he says.

He said this Thursday, at the beginning of a five-day round of receptions: lunch at the New York City Bar Association, with writer E.L. Doctorow and Random House chief Robert Bernstein in attendance; a talk for the Dramatists' Guild at the downtown Joyce Theater, where, with lyricist Adolph Green and playwright Terrence McNally among the audience, he moved from questions regarding the price of capitalist theater to do a bit of mime; cocktails at the home of "Anarchist" producers Alexander Cohen and Hildy Parks; a whirlwind tour of seven Broadway shows, which allowed him 20 minutes each, and a look at rehearsals for his own. The costumes for some of the supporting players in his show were, he said, all wrong -- he confided that he had made a terrible fuss.

His own costume, as he began his round of engagements, was, like his style, distinctly nonrevolutionary. A stocky, white-haired man with a tendency to look off into the distance and smile, he wore a pale pink sweater beneath his traditional sports jacket, and what looked remarkably like L.L. Bean shoes. When he spoke, it was likely to be with humor. His wife, the apparent instigator in their political work, is the flash: tightly rolled-up jeans, oversized glasses, abundant clunky jewelry -- the Wertmuller look favored by Italian theatrical ladies of a certain age. (Hers is 55.) Given the opportunity, she'll talk for 30 minutes about prison reform, though with an openness that is charming.

"There was a time, when we were on the legitimate stage, I was so shy, I would not go to bathroom, I would hold it in rather than walk across the Plaza," she said. "But when I speak on prison I am hardheaded."

"We do not agree with people who are terrorists," she said, "but we defend even the rights of terrorists to have a pair of eyeglasses in prison if he needs them, to not be tortured physically . . ."

Theirs has been a long marriage, of 32 years, a marriage of the theater, a marriage in which sparks still fly. She was of a family of actors dating back to the 17th century; he was the grandson of a laborer, the son of a builder, with a degree in painting and studies in architecture that he threw over for a life on the stage. They met, they recalled in a relatively quiet moment at their hotel, on the stage.

"He was very shy," said Rame, getting up to act it out. "I watch him for two days, and then I throw him up against the wall, and I kiss him."

"This was just a technique, this shyness," said Fo, sitting back in a large armchair and watching his wife's performance with some pleasure.

"I am surrounded by tall, tall men, very beautiful, and instead . . . questo brutino, this small, ugly man," she said, as he laughed. "But he was molto simpatico, very sympathetic, and so I marry him."

"Two years later," corrected Fo. "She is very, very dramatic. She comes, she leaves me." He laughed. "Puttanesca," he said.

Their beginnings were, they say, on the legitimate musical stage, though one must understand that the musical, in Italy, is a satirical form, nothing like Broadway. In time, they say, they became increasingly political -- it was after the war, after all, after fascism, there were changes in the theater all over Europe. In 1968, a time of great political change, they decided to leave the legitimate theater "to serve the worker class."

They performed in private homes, town squares, the street, funding the troupe with all the money they had made in the past 10 years. And they were quite successful; they say they made a lot. When workers were laid off, they gave benefit performances. Prison reform became a cause after young people were beaten and arrested -- she has three children, Rame says, and she was concerned.

Of the visa problems, the couple say they believe their own government, as well as the American government, preferred they would remain in Italy -- they had done shows on Chile, they say, they had presented shows in Vietnam.

The biggest misconception the State Department has had about them, then?

"It is only because they don't know us," said Rame. "If they know us, we will be friends."

"It is the duty of every intellectual and every person who thinks to denounce what does not work, to encourage the people to take power . . ." said Fo.

And how does he feel about his play being produced on Broadway, the heart of capitalist theater?

"It's not the first time I have seen the show presented in a nonrevolutionary theater," he said. "Some of the worst performances have been done in the revolutionary theater."

And how does he hope the audience will respond?

"First of all, to have fun," he said. "And then to go home, with somehow a different view."