The numbers are going down even though military service now provides a fast track to American citizenship, an Associated Press review of military data shows.
The decrease in non-citizen enlistees, who hail from countries such as the Philippines, Mexico, Nigeria and Germany, has hit all branches of the armed services, which already are struggling with recruitment as the US presence in Iraq enters the third year.
While US citizen enlistments have also fallen, the drop is more pronounced among non-citizens - legal immigrants the military has long let serve as everything from cooks to front line soldiers, though not generally as officers.
Although the Pentagon has placed a heavy emphasis on recruiting, officials say they're not concerned about the enlistment dip among non-citizens.
The decline surprises immigration and military experts, who expected that green-card holders who might otherwise wait years to become Americans would jump at the citizenship offer President George Bush extended nearly three years ago.
Instead, the annual number of non-citizen enlistees has fallen nearly 20% from fiscal year 2001 - the last full year before the changes - to fiscal year 2004, according to military data.
Much of the decline happened
last year alone
Much of the decline, from 11,829 to 9,477 recruits, came last year alone.
By comparison, annual enlistments among citizens dropped 12%, from 264,832 to 232,957 recruits.
Some 142 non-citizen troops have died in Iraq and Afghanistan. Non-citizens' casualty rates represent 8% of the total despite being less than 3% of active duty military personnel.
Bush pitched citizenship not as a selling point but as a reward for service. Last year, more than 7,500 people already in uniform gained citizenship through the military, the highest numbers since the Vietnam War.
But potential recruits who are legal immigrants are less drawn to the offer, noting they can apply to be citizens without risking their lives.
America's roughly 30,000 foreign soldiers come from more than 100 countries, with the largest contingent living in California. More than a third are Hispanic.