PESHAWAR, Pakistan — A former prime minister, Benazir Bhutto, warned yesterday that “foreign forces” could enter Pakistan unless the government re-establishes control in tribal border areas that have become militant hotbeds since the American-led invasion of neighboring Afghanistan. The comments, made as Ms. Bhutto stumped in the troubled northern region for support in January 8 parliamentary elections, were an apparent reference to American and NATO forces operating on the Afghan side of the border.

“If Pakistan has no control in the tribal areas then tomorrow foreign forces can come there,” Ms. Bhutto told journalists in Peshawar, the capital of North West Frontier Province. Ms. Bhutto also said economic development was crucial to defusing the pro-Taliban insurgency in the impoverished north, where Pakistani soldiers have clashed with insurgents in areas that now include the once tourist favorite Swat valley, 100 miles from the capital, Islamabad. “We will use the military in the tribal areas, but we disagree that a military operation is the only solution to the problem,” Ms. Bhutto said. “The people of tribal areas are our own people. We want to bring them into the modern age by giving them progress and prosperity.”

Ms. Bhutto launched her campaign on Saturday, urging the people of Peshawar, a stronghold of religious parties, to forsake militancy and support her secular Pakistan People’s Party.

Other opposition parties have threatened to boycott the ballot unless President Musharraf reinstates several Supreme Court judges he fired after declaring emergency rule November 3. The opposition parties claim he chose replacements who would let the government rig the ballot.

A boycott would be a serious blow to American-backed efforts to return Pakistan to democracy after eight years of military dictatorship. Mr. Musharraf has said emergency rule will end December 16 — as demanded by Washington and the opposition.

Opposition groups and people in the tribal areas have sharply criticized the government’s reliance on the military to fight the insurgency, blaming Mr. Musharraf for acting as Washington’s proxy in the war on terror.

But Ms. Bhutto warned against allowing the insurgency to spread. “Whatever is happening in Swat and the tribal area today, that can come to Islamabad tomorrow. And will the world look on as spectators … [if] Kahuta falls into their hands,” Ms. Bhutto said, referring to the site of Pakistan’s main nuclear installation, located just east of the capital. Peshawar is a conservative city near the Afghan border, and Ms. Bhutto’s presence prompted a massive security operation involving hundreds of police and private guards.

Ms. Bhutto and another former prime minister, Nawaz Sharif, plan to meet soon to discuss the election boycott issue. She has said she will only boycott the vote if all opposition parties do the same.

Yesterday, Mr. Sharif led a rally of about 2,000 supporters through the eastern city of Lahore. Mr. Sharif denounced Mr. Musharraf, accusing him of blindly following Washington’s dictates.

“He is obeying America with his eyes shut,” Mr. Sharif said. “Let us join together to save Pakistan, because the nation is in a grave crisis.”

A coalition of six religious parties has also delayed a decision on a boycott and said it will consult with both Ms. Bhutto and Mr. Sharif, who is seen as Mr. Musharraf’s most implacable foe.

Mr. Musharraf overthrew then-Prime Minister Sharif in a 1999 bloodless coup. He was elected for another five-year term as head of state in October. On Wednesday, he stepped down as military chief and retired from the army.

On Saturday, six civilians died in an artillery barrage in North Waziristan, a tribal region along the border, an intelligence official said. The official, who spoke on condition of anonymity because he was not authorized to make media comments, said government forces had been shelling suspected militant positions near the region’s main town of Miran Shah when two homes were hit.

Major General Waheed Arshad, the army’s top spokesman, said troops had opened fire in response to a militant attack. He did not confirm reports of civilian casualties.