LAHORE, Pakistan, Aug. 22 — After months of widespread frustration with corruption, the economy and a lack of justice and security, doubts about President Hamid Karzai of Afghanistan, and by extension the American-led effort to rebuild that nation, have led to a crisis of confidence.

Interviews with ordinary Afghans and with foreign diplomats and Afghan officials make it clear that the expanding Taliban insurgency in the south represents the most serious challenge to his presidency to date.

The insurgency, along with the other issues, has brought an eruption of doubts about Mr. Karzai, who is widely viewed as having failed to attend to a range of problems. That has left more and more Afghans asking what the government is doing.

Corruption is so widespread, the government apparently so lethargic and the divide between rich and poor so gaping that Mr. Karzai is losing public support, warn officials like Ahmad Fahim Hakim, deputy chairman of the Afghan Independent Human Rights Commission.