Plan B has become Plan A in the Bloomberg administration’s stealth war on teen pregnancy.

Handouts of the “morning-after pill” to sexually active students have skyrocketed under an unpublicized project in which health centers in public schools offer girls a full menu of free birth-control drugs and devices, records obtained by The Post show.

Last September, the city revealed it had started giving out Plan B and other birth control in the nurses’ offices of 13 high schools. At the time, officials said 567 girls had gotten Plan B.

But the birth-control blitz was much bigger than the city had acknowledged. About 40 separate “school-based health centers” doled out 12,721 doses of Plan B in 2011-12, up from 10,720 in 2010-11 and 5,039 in 2009-10, according to the newly released data.

About 22,400 students sought reproductive care from January 2009 through last school year, records show. Under state law, minors don’t need parental OKs to get contraceptives.

The revelations stunned Mona Davids, president of the NYC Parents Union, whose 14-year-old attends a Manhattan high school.

“I’m in shock,” she said. “What gives the mayor the right to decide, without adequate notice, to give our children drugs that will impact their bodies and their psyches? He has purposely kept the public and parents in the dark with his agenda.”

Davids, who is black, noted that most school-based health centers are in poor neighborhoods.

“This was population control on blacks and Latinos without our knowledge,” she said.

Plan B, which can block pregnancy if taken up to 72 hours after sex, is just one weapon in the city Department of Health’s arsenal for its Reproductive Health Project, an internal report reveals.

Besides “emergency contraception,” about 40 school-based clinics have dispensed prescriptions for birth-control pills, intrauterine devices (IUDs), hormone-delivering injections and Patch and NuvaRing — covering a total 93,569 monthly cycles through June 2012, the report says.

The Post obtained the report under a Freedom of Information Law request.

Handouts of birth-control packets rose from 6,027 in 2009-10 to 10,462 last year. Depo-Provera injections rose from 1,213 to 2,117. Staffers also insert plastic IUDs in the uterus, where they can remain for years.

Officials refused to discuss the project.

The city says about 6,300 NYC girls under age 17 had unplanned pregnancies last year, and more than half had abortions. Of those who give birth, the city says, about 70 percent drop out of school, making their futures bleak.

The city “has been able to place NYC public high school [health centers] on the forefront of the delivery of sexual and reproductive health services,” the report says.

The city Bureau of Maternal, Infant and Reproductive Health launched the project with a grant from the Fund for Public Health in New York.

The school-based health centers run under contract with local hospitals. The city spent $2.7 million on the centers this fiscal year.

Students without health insurance get the birth control free of charge. A city-founded nonprofit prescription service, NYCRx, reimbursed the centers $390,861 for contraceptives last school year, the report says.