Brown wrote Thursday that he had seen the professionalism with which women serve in the military during his 32 years in the Army National Guard.

"It's time to break this brass ceiling," he said. "That's why I have encouraged Defense Secretary Leon Panetta to lift the prohibition on qualified women in combat and allow them to compete for the same jobs and opportunities currently available to men."

Brown has remained popular in Massachusetts despite being the only Republican in the state's congressional delegation by maintaining an independent, centrist stature, bucking his party occasionally on major issues. He used the op-ed Thursday to remind voters of another issue where he is more in line with President Obama and his state's more liberal electorate than he is with most of the GOP.

"I approach this issue the same way I did with respect to my vote in support of repealing the ban on gays serving openly in the military," Brown said. "When a soldier answers the call to serve, and risks life or limb, it has never mattered to me whether they are gay or straight, male or female."

Two recent polls show Brown with about a 10-point lead over Warren, the presumed Democratic nominee.