WASHINGTON  President Obama on Monday admonished President Hamid Karzai of Afghanistan that he must take on what American officials have said he avoided during his first term: the rampant corruption and drug trade that have fueled the resurgence of the Taliban.

As Mr. Karzai was officially declared the winner of the much-disputed presidential election, Mr. Obama placed a congratulatory call in which he asked for a “new chapter” in the legitimacy of the Afghan government.

What he is seeking, Mr. Obama told reporters afterward, is “a sense on the part of President Karzai that, after some difficult years in which there has been some drift, that in fact he’s going to move boldly and forcefully forward and take advantage of the international community’s interest in his country to initiate reforms internally. That has to be one of our highest priorities.”

The administration wants Mr. Karzai and the Afghan government to put into place an anticorruption commission to establish strict accountability for government officials at the national and provincial levels, senior administration officials said Monday.