WASHINGTON (AP) — The more than 400,000 National Guard and Reserve members mobilized since September 2001 for the fight against terrorism will be offered the choice of military health care coverage for as long as eight years after they return to civilian life, officials said Thursday.

Only those who remain in the Guard or Reserve after they are demobilized will be eligible, said Thomas Hall, the assistant secretary of defense for reserve affairs.

Hall said that in discussing the plan with more than 2,000 Guard and Reserve members in the Persian Gulf recently he heard a great deal of enthusiasm for this kind of transitional health insurance.

‘‘It targets the young men and women bearing the brunt today,'' Hall said.

Until now, Guard and Reserve members could retain health care coverage under the Defense Department's Tricare system for no more than six months after they left active duty.