TRENTON, N.J. — Merck & Co., bowing to pressure from parents and medical groups, is immediately suspending its lobbying campaign to persuade state legislatures to mandate that adolescent girls get the company's new vaccine against cervical cancer as a requirement for school attendance.

The drug maker, which announced the change yesterday, had been criticized for quietly funding the campaign, via a third party, to require 11- and 12-year-old girls get the three-dose vaccine in order to attend school.

Some had objected because the vaccine protects against a sexually transmitted disease, human papilloma virus, which causes cervical cancer. Vaccines mandated for school attendance usually are for diseases easily spread through casual contact, such as measles and mumps.

"Our goal is about cervical cancer prevention, and we want to reach as many females as possible with Gardasil," Dr. Richard M. Haupt, Merck's medical director for vaccines, told The Associated Press.

"We're concerned that our role in supporting school requirements is a distraction from that goal, and as such have suspended our lobbying efforts," Haupt said, adding the company will continue providing information about the vaccine if requested by government officials.

Merck launched Gardasil, the first vaccine to prevent cervical cancer, in June. It protects against the two virus strains that cause 70 percent of cervical cancer and two strains that cause most genital warts.

Sales totaled $235 million through the end of 2006, according to Merck.

Last month, the AP reported that Merck was channeling money for its state-mandated campaign through Women in Government, an advocacy group made up of female state legislators across the country.

Conservative groups opposed the campaign, saying it would encourage premarital sex, and parents' rights groups said it interfered with their control over their children.

Even two of the prominent medical groups that supported broad use of the vaccine, the American Academy of Pediatricians and the American Academy of Family Practitioners, questioned Merck's timing, Haupt said yesterday.

"They, along with some other folks in the public health community, believe there needs to be more time," he said, to ensure government funding for the vaccine for uninsured girls is in place and that families and government officials have enough information about it.

Legislatures in roughly 20 states have introduced measures that would mandate girls have the vaccine to attend school, but none has passed so far. However, Texas Gov. Rick Perry on Feb. 2 issued an executive order requiring Texas girls entering the sixth grade as of 2008 get the vaccinations, triggering protests from lawmakers in that state.

Parents in Texas could opt out for their daughters if they state religious or philosophical objections, but several lawmakers there want parents to opt in instead of being able to opt out.

Perry defended his order yesterday, a day after lawmakers in Austin held a lengthy hearing on the issue but failed to act on a bill to override the order.

Dr. Anne Francis, who chairs an American Academy of Pediatrics committee that advocates for better insurer reimbursement on vaccines, called Merck's change of heart "a good move for the public."

"I believe that their timing was a little bit premature," she said, "so soon after (Gardasil's) release, before we have a picture of whether there are going to be any untoward side effects."