The violence came as US National Security Adviser Jim Jones and CIA director Leon Panetta were in Pakistan to urge the government to step up pressure on militant groups following a botched May 1 car-bombing in New York's Times Square, a White House official said.
Pakistani forces have increased their attacks in the Orakzai and Khyber regions of the northwest in recent weeks after largely clearing Taleban strongholds in other areas.
The militants emerged out of forested mountains to attack the checkpoint in the Dobbari area soon after dawn, said a government official in the region, Nauman Khan.
“They first fired rocket-propelled grenades at our checkpost and then closed in and attacked," said a military officer in the northwest who declined to be identified.
"We responded quickly and repulsed the attack after fierce fighting which lasted about three hours," said the officer.
At least 40 militants as well as two soldiers were killed.
Twenty-two soldiers were wounded, he said.
There was no independent confirmation of the casualty toll and Taleban spokesmen were not immediately available for comment.
Nuclear-armed Pakistan joined the US-led campaign against militancy after the Sept. 11, 2001, attacks on the United States.
The militants intensified their attacks on the Pakistani state in mid-2007 after security forces cleared a radical mosque complex in the capital where militants had holed up with numerous weapons and refused to surrender.
A year ago, the security forces began a series of sustained offensives and managed to clear many fighters from the Swat valley, northwest of Islamabad, and the South Waziristan and Bajaur regions on the Afghan border.
In recent weeks, the army has turned its attention to the Orakzai and Khyber regions, where many fighters are believed to have taken refuge from the earlier offensives.
But despite losing ground, the militants have shown the ability to bounce back and have carried out a wave of bomb attacks, killing hundreds of people, mainly in the northwest.
Pakistani action against militants along the Afghan border is seen as crucial for US efforts to stabilize Afghanistan.
The United States wants Pakistan to go after Afghan Taleban factions who launch cross-border attacks on Western forces in Afghanistan from sanctuaries on the Pakistani side of the border.
The United States has increased pressure on Pakistan to send troops into North Waziristan, an Afghan Taleban stronghold on the Afghan border, following the a failed bombing in New York claimed by the Pakistani Taleban, who also operate in the region.
Jones and Panetta were visiting Pakistan to help make sure "all efforts are undertaken" to keep pressure on the militants, John Brennan, assistant to the president for homeland security and counterterrorism, said in Washington on Tuesday.
The two Americans met President Asif Ali Zardari and other political and military leaders, officials said.
Addressing a Washington conference, Brennan acknowledged differences with Islamabad about what next steps to take.
But he said US President Barack Obama was prepared to do "what we need to do to protect the American public,” suggesting Washington has not ruled out taking unilateral action in Pakistan if necessary.
