The day after her triumphant return from exile, Pakistani opposition leader Benazir Bhutto said she remains uncertain about the tactics she will use in her campaign to topple President Mohammed Zia ul-Haq, but insisted she would avoid violence.

Claiming that up to 7 million supporters throughout the country welcomed her return to Pakistan on Thursday, Bhutto declared yesterday that she could have chosen to take power by force, by directing the crowds to seize government institutions in Lahore, the country's second largest city.

She said the crowd , which independent observers estimated in the hundreds of thousands, "could have brought down this government . . . if it was our intention to have a changeover with bloodshed.

"The crowd in Lahore could have burnt down the assemblies, it could have burnt down the military cantonment, it could have burnt down the homes of ministers," she declared. "But my party will never permit such a change to come over because my party does not want to stand for violence."

Speaking at a press conference, Bhutto seemed prepared for a drawn-out campaign against Zia, who overthrew her father, former prime minister Zulfiqar Ali Bhutto, in a 1977 military coup. Bhutto, 33, appeared to position herself for an attempt eventually to isolate Zia from his own civilian government and from the United States.

The Harvard and Oxford-educated Bhutto also appealed indirectly for official U.S. support for her campaign against Zia. She played down strong anti-American sentiments expressed by supporters in her emotional motorcade from the airport to the city.

Bhutto said supporters of Zia's regime, seeking to turn American opinion against her and her party, were responsible for burning American flags in the motorcade. Most observers believe, however, that the flags were burned by left-wing militants of Bhutto's Pakistan People's Party, who are strongly anti-American. "It is better for countries that believe in freedom and justice to come out on the side of the people," she said, adding that recent U.S. actions in distancing itself from strongmen such as Haiti's Jean-Claude Duvalier and the Philippines' Ferdinand Marcos had alarmed Zia's supporters.

"Perhaps these people fear that when the people make their sentiments known, the dictator will not be bailed out, as the dictators of Haiti and the Philippines were not bailed out," she said.

Bhutto has spent most of the past nine years in exile or under detention in Pakistan. She returned to Pakistan last summer to attend a funeral for her slain brother and was put under house arrest briefly for alledged opposition activities but was permitted to return to exile in London.

Her supporters' fears for her safety rose early today after a man carrying papers identifying him as a retired Army major broke into her headquarters, beat up several servants and said he wanted to see Bhutto, who was sleeping in another house at the time. The man later told reporters, "My senses were not with me."

As Bhutto's daughter and political heir, she has come to symbolize Pakistan's lost democracy and is expected to resume the leadership of the country's main opposition party.

Although Bhutto demonstrated on Thursday that she remains a powerful political personality in the country, Pakistani and foreign observers discounted her claims that she could take power immediately. They suggested she must now demonstrate organizational skills to revitalize her divided party.

Bhutto insists that Zia -- who ruled through martial law for 8 1/2 years before establishing a civilian government last December -- must resign and allow national elections.

Bhutto declined to set a deadline for her demands, saying this would increase the risk of confrontation with the government and appeared either flexible or uncertain about the details of her demands.

Asked if she would require that Zia step down before an election, Bhutto replied, "I'm taking things step by step, I'm testing things, I'm learning from the masses and I'm giving a lead as I go along."