The move will not be publicly announced until Thursday and will take some time - possibly as long as three years - to implement, but it's clearly a landmark event in the centuries-long fight for women's equality in America.
The move is also a bit of a mind-bender - effusively praised by many liberals who've also marched over the years to have fewer Americans of any gender waging war overseas.
Timothy Lange, writing on the popular progressive blog Daily Kos, hailed the decision, noting that female soldiers have already been lauded for bravery under fire while serving in Iraq and Afghanistan. But he added: "Now, if only we could engage in fewer wars for them and men in uniform to fight."
The irony, of course, is that as female enlistment in the armed forces has increased over the last couple of generations while U.S. military operations have expanded overseas, women have already engaged in combat - and died. In fact, it's estimated that roughly 20,000 women have served in Iraq and Afghanistan, with more than 800 wounded and about 130 killed.
Indeed, the story of America's post-9/11 military actions are laced with tales of "womanity," of bravery like Capt. Allison Black, who - despite the restrictions - navigated an AC-130H gunship to fight off the Taliban in Afghanistan, and of loss like Cpl. Jennifer Parcell, who was making security checks of women in Iraq's Al Anbar province when one exploded a suicide vest, killing her.
In the 1970s, the notion that a woman like Parcell would die in a war was a main argument of those who led the successful fight to reject the proposed Equal Rights Amendment.
Now, the decision to be announced by Panetta - opening up as many as 238,000 front-line slots that were once reserved only for men - is clearly a victory for equal rights, without the capital letters. It ensures that more female soldiers and sailors will win well-deserved promotions to combat leadership roles and ultimately to top brass.
Still . . .
It feels kind of bittersweet that this is the biggest victory for women's rights in this generation - when we've devoted such little energy to ending the rampant spirit of militarism that has sent so many men and women into conflicts that have dwarfed World War II in length - wars that polls now show a majority of Americans think weren't worth it.
Maybe the thought of someone's daughter dying on the battlefield will make policymakers think twice before the next misadventure, but I doubt it.
Ironically, it was the likely new secretary of state, Sen. John Kerry, who famously asked in 1971, after fighting in Vietnam: "How do you ask a man to be the last man to die for a mistake?"
Time marches on. Today, we can ask ourselves: How do you ask a woman to be the last woman to die for a mistake?
On Twitter: @Will_Bunch