A federal judge has ordered the Defense Department not to block fast-tracked citizenship applications that it promised to about 2,000 foreign-born U.S. Army Reserve soldiers under their enlistment contracts.

The order Wednesday came in an ongoing lawsuit over the department's year-old effort to kill a program designed to attract foreign-born military recruits who possess medical or language skills urgently needed in U.S. military operations. In exchange for serving, those recruits were promised a quicker route to citizenship.

U.S. District Judge Ellen S. Huvelle of Washington issued a rare preliminary injunction saying that while the lawsuit can move ahead, the government cannot in the meantime withhold a form that three named Army plaintiffs and other military members in similar situations need to start the vetting for citizenship.

Huvelle in her order also said that the members of the military in the lawsuit probably would succeed in proving the Pentagon's latest moves in the crackdown on immigrant recruits were "arbitrary and capricious."

Her decision granted provisional class-action status to at least some affected U.S. service members and marked the first court ruling on the new policy that has been challenged in lawsuits across the country. The court action came less than two weeks after Defense Secretary Jim Mattis said the military was taking steps "to save the program, if it can be saved."

[The Pentagon promised citizenship to immigrants who served. Now it might help deport them.]

Defense officials have restricted the fast-track citizenship program, citing the "espionage potential" posed by foreign-born recruits, but advocates said the changes have deprived the military of urgently needed skills in ongoing conflicts, while putting the legal status of more than 1,000 recruits in jeopardy.

In a 35-page opinion issued Wednesday night, Huvelle said new Pentagon provisions threatened to delay soldiers' citizenship applications by years, upending their lives, blocking their careers and potentially exposing them to deportation.

"The record shows that [Department of Defense] . . . policy is causing irreparable harm to plaintiffs," Huvelle wrote. "Plaintiffs live in constant fear that they will lose their work or student visas, or be discharged, deported, and subject to harsh punishment in their country of origin for joining a foreign military."

[How the Pentagon ending its deal with immigrant recruits could hurt the military]

The Justice Department declined to comment, spokesman Devin M. O'Malley said Thursday.

The plaintiffs, Mahlon Kirwa, Santhosh Meenhallimath and Ashok Viswanathan, who have trained in the Army Reserves' Selected Reserves since at least January, and their attorneys declined to comment because of pending litigation, said lead attorney Douglas W. Baruch.

Huvelle is set to hear arguments Friday morning for a similar injunction against the Pentagon by a separate group of about 500 foreign-born reservists who earlier obtained military service certifications allowing them to apply for accelerated U.S. citizenship but whose applications face new, open-ended delays because of screening likened to that required for "Top Secret" security clearance, according to court filings.

[U.S. Army kills contracts for hundreds of immigrant recruits. Some face deportation.]

At issue is a program in which the Pentagon until this year typically approved within one day requests for an "N-426" form certifying the active-duty or Selected Reserve status of qualified enlistees in the Military Accessions Vital to the National Interest program. The MAVNI program since 2009 has allowed recruits with critically needed skills who agreed to eight years of military service to apply for citizenship when they begin training.

But the advantage of that quick application process at enlistment was lost when the Pentagon on Sept. 30 began requiring additional screening of program participants, citing national security concerns.

In court filings, the Defense Department acknowledged that as recently as Oct. 13, it had no formal written guidance on the meaning of "honorable service" required for the N-426 certification needed by service members as part of the citizenship application. But attorneys for the Defense and Justice departments argued that the federal court could not review what they deemed an internal Pentagon decision.

Huvelle rejected what she called "the curious argument" that new Pentagon guidance "was not subject to judicial review and required no explanation because no formal policy existed before."

Huvelle said the Pentagon's delays were "not justified by any national security concerns" because U.S. immigration authorities are holding all applications pending completion of military screening and that citizenship can be revoked if recruits are not honorably discharged.

Huvelle also blasted the department for the new policy, issued the same day as Mattis said he supported reactivating the program.

[The Pentagon tried to kill a program for immigrants. Mattis thinks it can be saved.]

"Facing the probability" that its actions would be found to be illegal, Huvelle wrote Wednesday, the U.S. government "changed course, offering a new set of criteria that would allow it to further" delay approving reservists' certifications.

"DOD offered no reasoned explanation for this change, thereby suggesting that DOD's

decision was an arbitrary and capricious one," Huvelle wrote. Before Oct. 13, "enlistees had a right to apply for an expedited path to citizenship and [now] DOD's new procedures rob plaintiffs of this opportunity."

The MAVNI program has produced more than 10,400 troops since 2009.

The Pentagon has also extended tighter enlistment regulations for U.S. permanent residents, or green-card holders, saying they must complete up to year-long background checks before arriving for training, reversing a policy that they could enlist and ship upon the initiation of checks.

Green-card holders are reliable recruits who stay in the military longer than those born in the United States, a 2011 study concluded. The study recommended that the services target this specific demographic as part of their recruiting efforts.

Margaret Stock, an Alaska-based immigration attorney and retired Army officer who led the creation of the program, called the changes poorly thought out and a reflection of "for whatever reason, the new leaders of the Department of Defense don't want immigrants in their ranks, and they don't want naturalized citizens to have careers in the military," in what she called a sea change in centuries of practice.

"Threats to national security tend to be individualized. You have to look at individual threats . . . You can't say everyone native born is not a threat, just as you cannot say every one born in a foreign country is a threat."

Alex Horton contributed to this report.