By Louis Charbonneau

UNITED NATIONS, Sept 3 (Reuters) - The U.S. ambassador to the United Nations on Wednesday defended himself against criticism from State Department officials who suggested he had had unauthorized contacts in Pakistan and Afghanistan.

Last week an email from Richard Boucher, the assistant secretary of state for South and Central Asian Affairs, in which he chided Ambassador Zalmay Khalilzad for planning to give "advice and help" to the husband of slain Pakistani Prime Minister Benazir Bhutto, was leaked to Washington reporters.

Bhutto's husband Asif Ali Zardari, viewed as being close to the United States, is seen as a strong candidate to take over from President Pervez Musharraf, who resigned last month.

Khalilzad confirmed that he had been in touch with Zadari but denied that there was anything improper about the contacts.

The ambassador said the contacts were far less frequent than last week's media reports suggested, adding that he had known both Bhutto and Zardari well for many years.

"These contacts have been social contacts for the most part and when something of a policy issue has been raised -- and those occasions have been very rare -- I have reported those to the Secretary (of State Condoleezza Rice) and to other relevant officials," he told reporters.

"I believe that these contacts are perfectly natural," he added. "I actually have been surprised by the commentary or characterization of those contacts."

In his strongly worded e-mail to the Afghan-born Khalilzad, Boucher demanded an explanation about why he had not been told in advance of the envoy's plans to see Zardari in Dubai.

Before coming to the United Nations, Khalilzad's was U.S. ambassador to Afghanistan and Washington's envoy to Iraq. Prior to his government career, he was an academic and taught international and public affairs at Columbia University.

He emphasized that he was an experienced person who knew how to draw the line between social and professional contacts.

"Just because I'm a government official now doesn't mean I should end those friendships and relationships that I've had with many people, particularly from the region of the broader Middle East, including Afghanistan and Pakistan," he said.

"These relationships have been useful for the United States," he added.

He also repeated previous denials that he planned to run for the presidency of Afghanistan and rejected suggestions that he was trying to undermine Afghan President Hamid Karzai.

"Let the records show that President Karzai and I are friends at least for decades," Khalilzad said.

In February, Rice mildly chastised Khalilzad for joining Iranian Foreign Minister Manouchehr Mottaki in a panel debate in Davos, Switzerland, the month before.

She summoned him to the State Department to explain his attendance at the meeting, which had not been cleared beforehand. The United States does not have diplomatic ties with Iran. (Editing by David Storey)

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