The attack will involve U.S. and international troops and will strike the Arghandab district, an area in southern Afghanistan just outside Kandahar, where some of the heaviest fighting has occurred.
Arghandab is considered the "Taliban's home," said U.S. Sen. Carl Levin, D-Mich., in a news conference Tuesday.
Levin and U.S. Sen. Jack Reed, D-R.I., recently returned from a trip to Afghanistan and Pakistan, where they met with top government and military officials.
Levin said the attack, which is scheduled for the end of the July or early August, will be "the Taliban's worst nightmare."
"This is going to be Afghan-led," Levin said. "The meaning of that will not be lost on the Afghan people and it will not be lost on the Taliban."
U.S. troops won't be spared the dangerous combat in Arghandab. The terrain is difficult and casualties are expected to be high, Reed said.
"We have very serious fighting ahead," Reed said.
An additional 30,000 U.S. troops will be deployed over the summer to help fight the surge in the southern region of the country.
The senators pointed to improvements in the Afghan army as progress in the 9-year war. Levin said the Afghan army has been actively recruiting since the announcement by U.S. President Barack Obama that the United States will begin withdrawing troops in July 2011 and turn responsibility over to Afghan forces. Levin confirmed Tuesday that the United States was on schedule for meeting that deadline.
Pakistan terrorist groups continue to pose a threat to U.S. and international forces, Levin said. Terrorist organizations, including the Pakistan-based Taliban and the Haqqani network, have launched attacks over the border into Afghanistan. The Pakistan government has failed to take action against the terrorist groups, Levin said.
Levin said he would ask the U.S. State Department to add both organizations to the list of foreign terrorist groups.
"It's long overdue," he said.
With the terrorist organizations added to the state department list, U.S. law would require Pakistan to take action against them, Levin said. If Pakistan didn't cooperate, the United States could restrict or revoke aid to the country, or even strike against the terrorist groups from inside Pakistan.
"Their country is used as the launching platform for terrorist attacks," Levin said.