WASHINGTON — Reservists on temporary duty overseas for more than a month will be allowed to use military medical facilities for routine care, under a policy change announced this week.

Defense health officials said the expanded medical care will be available to any reservists or guardsmen on temporary duty orders overseas for at least 31 days but fewer than 180 days.

Previously, those troops could visit military doctors or dentists only in emergency situations, and had to seek outside doctors and dentists for regular check-ups or other basic medical services.

Guard and reserve troops on active duty already have full use of those overseas facilities.

The new policy won’t go into effect until early spring, according to Chris Hober, spokesman for Tricare’s overseas programs. Overseas managers must work out exactly how the funding and paperwork details will work, and that will likely take several more weeks.

“But once that’s done, anybody who is near a [military treatment facility] who is on TDY for 31 to 179 days will be able to enroll there,” he said.

The decision was made to bring reserve and guard policy in line with other benefits, including those troops’ families are eligible for, Hober said.

Under current department policy, families who live overseas with reservists on temporary duty are eligible to use the overseas military treatment facilities after 30 days, even though their servicemember wasn’t covered for such appointments.

Hober said the new policy erases that coverage quirk, establishing the same rules for the troops and their families.

Servicemembers on temporary duty for 30 days or fewer won’t receive the new benefit, Hober said, but they still will be eligible to use those overseas base clinics in emergency situations.

Defense health officials said about 4,000 reservists on temporary duty in Europe would be affected by the change. Pentagon officials could not provide a more detailed breakdown of reserve and guard members worldwide who might be affected.