Giving girls as young as 9 a first-ever vaccine that blocks infection by four types of human papillomavirus could slash global deaths from cervical cancer by more than two-thirds, Merck & Co. officials said Thursday in seeking federal approval.

The vaccine, called Gardasil, protects against the two types of human papillomavirus, or HPV, believed responsible for about 70 percent of cervical cancer cases. It also protects against two types that cause 90 percent of genital wart cases.

Company officials, in making their case for approval to members of a Food and Drug Administration advisory panel, implied that Gardasil could be the biggest advance in preventing cervical cancer since the pap test.

"Gardasil has the potential to meet an unmet medical need as the first vaccine to prevent cervical cancer," Merck's Dr. Patrick Brill-Edwards told members of the FDA's Vaccines and Related Biological Products advisory committee.

HPV is the most common sexually transmitted disease, affecting more than 50 percent of sexually active adults. The cervical cancer it can cause kills each year roughly 290,000 women worldwide, including 3,500 women in the United States, where regular pap smears often detect precancerous lesions and early cancer.

Merck said the vaccine could be used in females between the ages of 9 and 26, but would work best when given to girls before they begin having sex.

"It will be most effective when administered prior to entry in the risk period, and that is the age group 15 and below," Merck's Dr. Eliav Barr told the panel.

The FDA advisers were to decide late Thursday whether to recommend FDA approval for the vaccine. The FDA isn't required to follow the advice of its expert panels but usually does. A decision is expected by June 8.

FDA reviewers said Gardasil appears safe and effective, but cautioned that it may lead to an increased number of cases of a cancer precursor among patients already infected by any of the four virus types at the time they receive the vaccine, and whose immune systems have not cleared the virus from their bodies.

Furthermore, any advantage the vaccine provides in protecting against the four virus types could be offset by infection by any of the multiple other types of HPV that the vaccine does not cover, according to FDA briefing documents. FDA staff also asked that the committee examine five cases where children with birth defects were born to women who had received the vaccine around the time of conception.

Whitehouse Station, N.J.-based Merck developed the vaccine and tested it in more than 27,000 females and males. Thursday's discussion focused on its use in preventing HPV-related disease in women.

Pending FDA action, the national Advisory Committee on Immunization Practices will decide later in June whether to endorse routine vaccination with the vaccine. The committee's HPV vaccine workgroup is recommending the vaccine be given to girls 11 and 12, and the committee will consider recommendations for females 13 to 26.

Widespread vaccination could help bounce cervical cancer from its dubious distinction as the No. 2 cancer in women worldwide. However, the anticipated cost of the vaccine, administered in three shots over six months, is $300 to $500 and could pose a barrier to that goal.

Early opposition to Gardasil, based on concerns it could encourage sexual activity in the young, largely dissipated, in part because of the vaccine's cancer-reduction implications.