Rep. Geraldine A. Ferraro (D-N.Y.), pronouncing herself "a one-woman truth squad," today derisively called President Reagan "Mr. Leader of This Country" while relentlessly attacking his handling of the Sept. 20 bombing of the U.S. Embassy annex in east Beirut.

In a citizens' forum downtown, the Democratic vice-presidential nominee noted that Reagan recently accepted responsibility for the suicide-attack but said: "It doesn't close the matter. People are dead. If you take responsibility, tell me what that means, Mr. Leader of This Country."

In a subsequent news conference, Ferraro also had harsh words for the Republican advertising campaign when asked why Reagan appears to have such a commanding lead.

"Look at the amount of money being spent on the ads. And if you can keep those ads going over and over and over . . . . It's almost like brainwashing," she said.

She took special offense at a current television ad in which the Republicans contend that Walter F. Mondale's tax increases would cost the average American family $1,800 a year. Ferraro said the assertion would be true only if the average family had an annual income of $90,000.

And when asked about recent disclosures that Vice President Bush paid the Internal Revenue Service nearly $200,000 in back taxes, Ferraro alluded to the controversy and grueling news conference in August about her finances.

"I don't know about the vice president's tax returns. In fact, I think that might be a question that you might ask him during his hour and 45-minute press conference with 200 of the press quizzing him about his financial statement," she said.

Earlier in the day, in Huber Heights, Ohio, Ferraro trooped out to a rural toxic waste dump to condemn the Reagan administration's environmental record while promoting her vision of a clean America.