WASHINGTON (Reuters) - President Barack Obama said on Thursday he supports a controversial decision by the U.S. health secretary to overrule government scientists about access to an emergency contraceptive known as the morning-after pill.

Obama said he backs Wednesday's decision by Health and Human Services Secretary Kathleen Sebelius to trump the Food and Drug Administration's plan to do away with the age limit on who can buy Teva Pharmaceutical Industries Ltd's Plan B One-Step pill without a prescription.

"When it comes to 12-year-olds or 13-year-olds the question is can we have confidence that they would potentially use Plan B properly?" Obama said.

He said he was not involved in the decision and was not contesting that it was safe for women to purchase.

But rather, he said, it was important to apply "common sense" to rules when it comes to over-the-counter medicine.

Girls under age 17 need a prescription to buy the drug, which has to be taken within 72 hours of unprotected sexual intercourse. It has been available without a prescription to women over 17.

Women's health advocates said the ruling goes against Obama's pledge to reassert the power of science in his administration's decisions.

Critics say the pill could lead to promiscuity, sexual abuse and fewer visits to the doctor if it is readily available for purchase.

Advocates for such emergency pills say they help reduce unwanted pregnancies or abortions and that quick, easy access for women of all ages is critical.

(Reporting by Jeff Mason and Tabassum Zakaria)