* Significant Waziristan operation seen
* Campaign pressures al Qaeda and Taliban
* Next target is suicide bomber kingpin
WASHINGTON, June 12 (Reuters) - Pakistan's military looks set to mount a significant combat drive in the Taliban stronghold of Waziristan, U.S. officials said on Friday and praised Islamabad's resolve against Islamic militants.
Several U.S. defense officials told reporters in Washington the Pakistanis were completing an offensive begun in April in the Swat valley and moving to a new phase aimed at isolating militants in other restive parts of northwestern Pakistan.
"The operations that appear to be underway now would be the largest operations that have been undertaken in Waziristan," said one official, speaking on condition of anonymity.
The official said the Pentagon anticipated "fairly significant combat operations in South Waziristan" aimed at the network run by Pakistani Taliban leader Baitullah Mehsud, one of the main sources of suicide bombers that have plagued Pakistan.
"We think that the initial phases of that operation have already begun," said the official, adding that "We are pleased that this level of force is being contemplated."
Pakistan's military went on the offensive in Bannu district on Tuesday after some 800 militants infiltrated from nearby Waziristan, a hub of Taliban and al Qaeda activity.
U.S. officials, worried that the Taliban could drive nuclear-armed Pakistan into chaos, have welcomed the Swat offensive and see the move into Waziristan as a sign Pakistan has become galvanized against the militants.
Taliban and al Qaeda leaders "are under very significant pressure," said a senior U.S. defense official.
"The Pakistani operations in Swat have contributed to that pressure and prospective operations in South Waziristan ... will add to that," he added.
"Even moving outside a given area -- meaning local area -- is quite challenging for them," the official said.
CHILD BOMBERS FOR SALE
Militants have launched a wave of bomb attacks in recent days in response to the army offensive in the Swat region, prompting Pakistani President Asif Ali Zardari to vow on Friday to fight against militancy "to the end".
In the latest bomb attacks, a prominent anti-Taliban cleric who had condemned suicide bombings was killed on Friday in a suicide attack at his office in the city of Lahore.
The first U.S. official warned that "isolated pockets of resistance still remain" in parts of the Swat valley as the Pakistani army worked to finish the two-month campaign and that Islamabad needed to brace for more attacks.
Taking out Mehsud, who can muster thousands of fighters, could help curb suicide attacks, said a third U.S. defense official.
"He has turned suicide bombing into a production output not unlike Toyota outputs cars," said the official, who described the militant warlord leader as leading an extensive network of militant madrassa schools that sold or bartered child suicide bombers in Pakistan's Northwest Frontier Province.
U.S. officials have expressed satisfaction recently that the bomb attacks appear to be hardening Pakistani public opinion against the militants and in support of military campaigns.
But the U.S. officials said that while Pakistan is keen on fighting domestic enemies that threaten its stability, it was less eager to challenge the international militants that take haven on its soil and threaten Afghanistan and beyond.
"Pakistan compartmentalizes the various militant threats" into groups that might be a useful hedge again rival India, those that might advance its interests in Afghanistan and internal threat, said the third official.
"We haven't seen anything to indicate a strategic reorientation in Pakistan thinking at this time," he said.
Editing by Philip Barbara
Our Standards: The Thomson Reuters Trust Principles.