* Obama critical of weak Afghan, Pakistan leadership

* Pakistan still views India as main threat - experts

* Senators seek $7.5 billion Pakistan aid package

By David Alexander

WASHINGTON, May 4 (Reuters) - President Barack Obama presents his strategy for defeating al Qaeda to the leaders of Afghanistan and Pakistan on Wednesday amid growing U.S. concern that it is losing the war and neither is a reliable ally.

The White House meetings with Pakistani President Asif Ali Zardari and Afghan President Hamid Karzai are likely to be cagey affairs -- both visitors have been heavily criticized by Obama's administration and are also wary of each other.

Equally, Obama's new strategy for defeating al Qaeda and Taliban militants operating in Afghanistan and Pakistan has not been universally welcomed in either country.

It will be Obama's first face-to-face meeting with the two men to discuss his new regional strategy and is a chance to air his concerns about corruption and poor governance.

One of the biggest challenges will be to convince Pakistan to take the threat of Islamist militancy seriously and prevent the Taliban from using its soil to attack Afghanistan, a major bone of contention between Islamabad and Kabul.