On some other official visits, protocol has required Michelle Obama to stand beside some other visiting spouse, with the hostess a full foot taller and a generation younger than her guest. This time, equality is evident.

Both the first lady and her British guest, Samantha Cameron, wore long gowns. Obama’s was a deep teal, open-necked, floor-length number by British-born Marchesa designer Georgina Chapman, who attended with her husband, Harvey Weinstein. And Cameron covered her shoulders and neck in a sparkly, patterned, belted dress also deeply blue, by the Italian-born and London-based Alessandra Rich.

“Very pretty!” the president admired, as Cameron stepped from limo to North Portico stairs. And to Prime Minister David Cameron, he observed: “They look better than us.” The Briton agreed with the smart combined assessment.

Side by side, there was no glamour disparity between the two women.

It was this way all day, ever since Michelle Obama and Samantha Cameron stepped into the early spring sunbeams on the White House lawn with ample confidence.

Cameron and Obama, both 40-something moms, have done what’s required of world-leader wives: to uproot family, to stall career, to grip and grin and bear it. Their morning role, like the evening duty, was to add to the waves and smiles of Wednesday’s Power Quartet tableaux. The vibe is very double-date, reminding spectators that the world has new leaders, and you’re lookin’ at ’em.

In the super-sunny morning, Obama wore a Zac Posen suit, its monochrome tone suggesting London fog. As luck would have it, the same color, approximately, appeared on the torso of Cameron’s blouse. The blouse was framed by turquoise sleeves, ending well above the wrist. Squint and you could find an all-American reference: the baseball practice T-shirt. But this is no Little League, and the image-conscious visit could be mined for many a sporty, cross-cultural shout-out.

Take the Tuesday afternoon outfits. At an American University event in honor of the “Let’s Move” fitness initiative and London’s 2012 Olympic Games, the political wives tromped on the gym floor in heels and trousers. As they swung at tennis balls, Obama’s pants were as creamy and flowy as Cameron’s were dark and fitted. The first lady wore another of her signature cardigans, this one by L’Wren Scott, the leggy Utah native who wound up involved with (if still not betrothed to) a British royal of sorts, Mick Jagger.

As a balm to mutual headaches such as China trade and Iranian uranium Tuesday evening, President Obama (referred to early and often as “Barack” by his counterpart) escorted Prime Minister Cameron (a.k.a. “David”) deep into Rust Belt, swing-voter territory and deeper into an Obama-era obsession — college hoops. The president ditched tie and jacket to talk brackets and alley-oop. The prime minister traded his V-neck sweater for a black polo shirt and confronted March Madness and a meaty hot dog.

Samantha Cameron has shown repeatedly that fashion may have been her occupation, but it’s not her preoccupation. Long a major force at the stationer and accessory-maker Smythson, she has gone from full-time creative director to part-time creative consultant. It looks as if she is dedicated to thrift as well as flair: She wore the same pink Roksanda Illincic top at American University that she had worn over a long skirt at London Fashion Week. The shoes and belt she wore both days looked to be un-regal repeats. Message, if you need one: This is a pack-light, wear-till-repair kind of era, on both sides of the Atlantic.

Elizabeth McGovern, who presides over “Downton Abbey” on PBS, was among the few state dinner guests who approached the wattage of the two leaders’ wives. Along with curly bangs and red lipstick, she wore something black and gauzy by Jacques Azagury.

Both Michelle Obama and Samantha Cameron have chosen looks that feature promising designers from the New York and London fashion weeks, respectively. They are gowns that show off not only a designer’s ingenuity, but also a first lady’s fearlessness. And Samantha Cameron stands shoulder-to-shoulder in stature.