Almost from the beginning of the conflict in Iraq, there has been an irresistable temptation to find, or refute, similarities to the one 40 years earlier in Vietnam.

There is one distinct difference, though.

In the 1960s, as the fighting in Southeast Asia ramped up, conscription was clearly on the minds of American men of Selective Service age. Many accepted the “Greetings” when they came; many even enlisted. But others sought deferments as students or conscientious objectors. Some burned their draft cards, some went to prison and some just fled the country.

Despite all the resistance, President Lyndon Johnson could keep replenishing and enlarging the U.S. troop presence in Vietnam, thanks to the draft. Today, there is no draft.

Or is there?

U.S. military personnel in today’s “all-volunteer” military can be required to stay in the service even after their enlistment periods have expired. As of Dec. 31, more than 10,700 soldiers were being kept in the Army beyond the period they had agreed to. Other branches are holding thousands more.

The Pentagon calls it “stop loss,” but critics such as Republican Sen. and ex-POW John McCain call it a backdoor draft, and it’s been going on since shortly after the invasion of Iraq almost four years ago.

Fortunately, Defense Secretary Robert Gates seems to recognize something his controversial predecessor Donald Rumsfeld didn’t: Stop loss poses serious political liabilities.

Although Gates just announced that commanders in Iraq will be assured the troops they need, and although President Bush’s call for a troop surge would require five more brigades, the secretary has directed all branches of the U.S. military to come back to him by Feb. 28 with plans for minimizing the use of stop loss.

That will be a daunting challenge for a military structure that:

“Had so much difficulty meeting recruiting quotas in 2005 that the percentage of enlistees who could be accepted despite low aptitude scores was doubled.

“Is rotating some units, including many in the Reserves and National Guard, back into the combat zone for two, three and more deployments.

“Disallows openly gay people from serving.

Stop loss has been available to the Pentagon since shortly after 1973 when, as the Vietnam War ground to a clumsy close, the United States ended the draft. But it wasn’t until 1990, with the Persian Gulf War looming, that the Defense Department employed the mechanism that was designed as a protection against running out of critical skills during a time of tactical need.

Now it’s routinely used because the Bush administration’s war against terror has overwhelmed the leaner military structure favored by Rumsfeld and others in the neo-con movement that pushed for the occupation of Iraq.

The growing domestic opposition to the Iraq war does evoke comparisons with Vietnam. And while there isn’t a draft to enflame domestic tension, the unfair treatment of volunteer troops represented by stop loss may serve the same purpose. Once Gates hears back from the service branches in a month, he needs to slam the backdoor draft shut.