Just as it began to appear that President Obama was moving toward adhering to his Afghanistan commander's call for 40,000 or more additional American troops, he has been unexpectedly confronted with an influential note of caution from his ambassador in Kabul. It only complicates the White House tug-of-war that has put critical policy-making on hold for months now.

In cables to Obama, Ambassador Karl Eikenberry has cast serious doubt about the wisdom of greatly enlarging the U.S. military footprint in the country, at a time American confidence in recently reelected President Hamid Karzai is in a precarious state.

That concern was clearly reflected Wednesday in a White House statement released after Obama's eighth closed meeting with his national security team on the way forward in Afghanistan. "The president believes that we need to make clear to the Afghan government that our commitment is not open-ended," it said. "After years of substantial investments by the American people, governance in Afghanistan must improve in a reasonable period of time."

The harsh tone was an obvious shot at Karzai's credibility in the wake of the fraud and corruption that marred his reelection, and an expression of the administration's impatience with him as Obama was about to embark on a nine-day Asian trip. Eikenberry's doubts signaled the probability that no decision on the troop level would come until Obama's return.

The American ambassador's concerns appear likely to put the brakes, at least for a time, on a go-ahead on Gen. Stanley McChrystal's request for a troop surge in Afghanistan, or one of lesser dimensions. Secretary of Defense Robert Gates is said to favor somewhat fewer U.S. military and more NATO troops. Others, including Vice President Joe Biden, want even fewer, with concentration on al-Qaida and other terrorist groups rather than the Taliban.

Eikenberry, who has considerable credentials for being heard, appears to have thrown a late lifeline to the Biden approach. The retired four-star general was a former U.S. commander in Afghanistan, plucked from his job as a top NATO command officer by Obama in April to take over the American embassy in Kabul.

From the start of Obama's reassessment of the American engagement in Afghanistan, which he has called a "war of necessity" unlike the one in Iraq whose invasion he opposed, Biden has been cited as the leading advocate for refocusing on the pursuit of Osama bin Laden and the eradication of al-Qaida, as the legitimate response to the 9/11 terrorist attacks. In recent weeks, his case against more troops against the Taliban appeared to be eroding, until the Eikenberry messages apparently generated the latest White House statement.

Obama's deliberate approach continued at a time the peril to American military men and women has particularly dominated the news. U.S. casualties in Afghanistan are at a record high. Americans have been shocked by the shootings at Fort Hood by an Army medical officer of Muslim faith reportedly opposed to the American involvement in Afghanistan.

Eikenberry's reservations became public on Veterans Day as Obama went to Arlington National Cemetery, laying a wreath at the Tomb of the Unknowns and walking among the white tombstones in Section 60, where many American soldiers and marines killed in Iraq and Afghanistan are buried. The president has defended the extended time spent in the Afghanistan troop reassessment with references to the high price paid, and to be paid in the future, by more Americans in both Middle East conflicts.

More than four decades ago, another American president, Lyndon B. Johnson, was confronted with the request of another general, William Westmoreland in Vietnam, for 200,000 additional U.S. troops. That expansion of the American involvement failed to end the bloodshed and by the time the U.S. forces withdrew, 58,000 Americans had died.

That history weighs heavily on Obama now, when public-opinion polls report a majority of Americans at home now believe the war in Afghanistan is not worth fighting. These factors explain why he agonizes so long over what to do at a critical crossroads in U.S. foreign policy.

Reach Jules Witcover at juleswitcover@earthlink.net.