He is a black-market profiteer who worked to help Iran and North Korea acquire the nuclear weapons secrets that President Bush (search) said makes them part of an "axis of evil."

Yet when scientist Abdul Qadeer Khan (search) received a public pardon Thursday from Pakistan's leader, there was nary a murmur of protest -- in fact there was praise -- from American officials.

To weapons inspector David Kay (search) and others, it was an outrage.

"I can think of no one who deserves less to be pardoned," said Kay, former head of a U.S. team that searched for weapons of mass destruction in Iraq. He said Khan was "running essentially a Sam's Club" of weapons technology.

Yet others say the public response may mask U.S. officials' real motivation.

What they are hoping, according to American officials speaking on condition of anonymity, is that Khan's pardon becomes a plea bargain of sorts, with Pakistan trading leniency in exchange for Khan's information about the still-at-large members of the worldwide nuclear black market.

"We could beat our chests and be outraged," said Robert Oakley, a former ambassador to Pakistan who defended the Bush administration's low key response.

"The most important thing is to get as much information possible as to where the links (to accomplices) were," Oakley said. "We have to make sure it doesn't happen again."

More than anything, the U.S. response shows just how solicitous American officials remain toward Pakistan President Gen. Pervez Musharraf (search), that they're leery of any public criticism lest it destabilize this key ally in the war on terrorism.

Any push by Musharraf for a trial of Khan could have led to a political showdown with Islamist and opposition groups who regard the scientist as a hero for founding Pakistan's nuclear weapons program.

Pakistan, which shares a border with Afghanistan, says it has arrested more than 500 Al Qaeda (search) followers since 2002. Many have been handed over to the United States.

U.S. officials also praise Musharraf for his role in arranging peace talks with India starting on Feb. 16, the first such discussions in over two years.

Above all else, U.S. officials often say that if Musharraf were to be toppled, the alternatives -- in a country with strong nationalistic sentiment, powerful currents of Islamic extremism and nuclear weapons -- could only prove worse.

So for now, U.S. officials seem willing to publicly accept Musharraf's assurances that he will prevent further proliferation of nuclear secrets, even though some critics believe Pakistani military or intelligence officials might have helped Khan.

At the United Nations in New York, Secretary of State Colin Powell (search) said he would talk to Musharraf by telephone over the weekend to make sure "there was no possibility" that remnants of the Kahn network would survive.

Powell did not criticize the president for pardoning the scientist but instead registered understanding. "He felt it was important for him to do," Powell said.

Similarly, U.N. Secretary-General Kofi Annan, at a separate news conference, said, "Obviously, it is a difficult situation he has to deal with."

State Department spokesman Richard Boucher credited Pakistani authorities with pursuing the investigation seriously ever since Iranian officials told U.N. nuclear experts more than two months ago about the leakage of secrets.

"We think that Pakistan is taking serious efforts to end the activities of a dangerous network," Boucher said.

Another official, speaking on condition of anonymity, said, "This is not about punishment. ... The Pakistanis have to use the most effective techniques to cut off this proliferation. There are others involved."

CIA Director George Tenet said Thursday that Khan's network "was shaving years off the nuclear weapons development timelines of several states, including Libya" and "offering its wares to countries like North Korea and Iran."

The International Atomic Energy Agency (search), the U.N. nuclear watchdog, gave Pakistan information that Pakistani technology had been found in Iran and Libya.

In the case of North Korea, however, Khan is believed to have begun providing sensitive technology only well after the country had developed the capability to produce plutonium-based nuclear bombs.

Nevertheless, said Daryl Kimball, executive director of the private Arms Control Association (search), "What has been revealed about Dr. Khan is perhaps the most egregious example of nuclear proliferation in the nuclear age."