WASHINGTON — The Obama administration said today three million Americans signed up for Medicaid under the new health care law as of the end of February, offering its first accounting of how much the safety-net health program has grown since implementation of the law.

Many were newly eligible because of the law’s Medicaid expansion.

The number is significantly lower than how many people the administration previously said were, quote, “determined eligible” for Medicaid under the law. But the new number sifts out duplicate applications to arrive at a solid figure.

The total is incomplete because a handful of states didn’t report their numbers, and it doesn’t include March sign-ups.

About half the states have accepted a Medicaid expansion in the health law.