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Rick Santorum's comments that " the front line of combat" is not the best place for women appear to put the Republican presidential candidate on the other side of public and expert opinion.

A number of recent studies have concluded that the U.S. military should stop excluding women from ground-combat units, which some believe denies them a chance to climb the ranks as quickly as their male counterparts.

Three-quarters of Americans believe that women should be allowed to engage in direct combat, according to an ABC News-Washington Post poll released in March, a sharp rise from the early 1990s when only 45 percent supported such a move. Politically, Democrats and independents are more in favor of lifting the restrictions but even a majority of Republicans, 62 percent, thought this should be the case and the poll found that in no political group was a majority opposed.

The Pentagon Thursday announced that it will end a decades-old rule and allows women to serve in battalions closer to the front lines. The changes would open up 14,000 support jobs to women in ground- combat units.

The new rule still bars women from serving directly in combat roles. But given the technology and the landscape today, many observers say those lines are blurred. Women already serve in dangerous support roles in war zones such as Afghanistan, as pilots flying combat aircrafts or on combat ships. In recent years, two women have been given the prestigious Silver Star for valor in a combat zone.

A study by the Rand Corporation in 2007 found that support units in which women were serving were connected with direct combat units based on proximity and that some who were returning from the battlefield in Iraq believed that the military's current policy, if implemented strictly, was "a backward step in the successful execution of the mission" and that it "could even prevent women from participating in Army operations in Iraq, which would preclude the Army from completing its mission."

A review by the Military Leadership Diversity Commission last year concluded that restrictions on combat roles "seems obsolete" in today's age. Another study in 2008 by the Strategic Studies Institute stated that "The nature of the current battlefield makes it impossible to apply strictly the existing rules for excluding women from combat without serious reduction in combat capabilities, degrading the professional development and thus status of women, and producing a potentially serious reduction in overall readiness."

Adm. Eric T. Olson, the top commander of U.S. special operations and a Navy SEAL himself, told ABC News in July that he's ready to see female SEALs in combat roles.

But some experts say the recent studies focus on diversity but don't take into account the realities on the ground.

Elaine Donnelly, who served as a member of the 1992 presidential commission on the assignment of women in the armed forces, says it's a cultural issue and that Santorum's concerns are legitimate. The commission voted against sending women in close combat because "that would like being an endorsement of violence against women," she said.

"It's not an equal opportunity or diversity issue. It's a matter of effectiveness," Donnelly, president of the Center for Military Readiness, told ABC News.

If a soldier is injured and his support soldier is a woman, "that man dies because she's not going to be able to meet the physical requirements and it doesn't matter how brave and courageous she is. … We respect women in the military but when you're talking about direct ground combat, if you start making diversity the most important factor, then you put lives at risk."

Women were barred from partaking even in non-combat positions until 1994, when President Bill Clinton's defense secretary, Les Aspin, lifted that rule.

The number of women in the military has jumped since the 1970s, when the United States ended the draft. Since 1973, the number of women who have joined the military has risen rapidly. The share of women among the enlisted ranks has increased from 2 percent to 14 percent, and the share among commissioned officers has jumped 4 percent to 16 percent, according to a study by the Pew Research Center.

The Pentagon wouldn't comment directly on Santorum's comments, but spokesman George Little said there's "a broad consensus" in the military that they should maintain the goal of opening more positions to women.

"I believe that men and women can serve ably on the battlefield men and women of the U.S. military are focused on the mission and in protecting our nation's interest. And I think that's a value that we have regardless of gender," Little said today. "The presumption is that going forward that we're going to find as many opportunities for women as possible."

As of Sept. 30, women comprised roughly 15 percent of the U.S. armed forces, with their numbers reaching 205,000. Of the 2.4 million ever deployed in support of Iraq and Afghanistan, 280,000 have been women and 144 of them have been killed in those two countries while 865 have been wounded.

A number of U.S. partners in the battlefield allow women to serve in combat roles, including Canada, Israel, France and Germany.

ABC News' Luis Martinez contributed to this report.