A lightness of countenance has fallen on Washington. I kid you not. Strangers were talking to each other in elevators, smiles in the street made walking a pleasure.

Even President Obama lightened up. At his midweek press conference, the president seemed in an unusually good mood: helping NBC’s Chuck Todd sort out his questions, referring cheerfully to the work ethics of his daughters (and his own), and lampooning the corporate jet set.

Had peace broken out somewhere? On Capitol Hill, in Libya or Afghanistan, between Los Angeles Superior Court judge Stephanie Sautner and Lindsay Lohan — her honor dropping by for a few belts?

No. It all comes down to the prospect of a four-day weekend. It should be three days, but many are able to stretch it to four. Heapings of happiness!

By the joy this little perturbation in routine has wrought, it’s clear that Americans are overstretched, overworked, overstressed and badly in need of R&R — even just a syllable of it — over the Fourth of July weekend.

Also it’s a birthday bash. Uncle Sam has made it through another year and the dollar is still worth having; the barbecue worth lighting; and the hamburger, America’s great contribution to cuisine, worth eating. Even though Budweiser — like so much else nowadays — belongs to a foreign company, millions of us still find it worth drinking.

Hooray! Happy Birthday! For he’s a jolly good fellow! (Uncle Sam, that is).

Unlike many others of the British persuasion, as I once was, I agree with my colleague Martin Walker that Brits shouldn’t feel loss on the Fourth of July, but should be leading the celebration.

Walker, who knows a thing or two about celebrating, says: “I’m not downcast by the victory of honest British colonial farmers over a German king and his German mercenaries.”  

That’s right, Americans love the Brits. Otherwise, why would a country that threw off the imperial yoke on July 4, 1776, go bats for the wedding of Prince Harry, heir to the despised throne once occupied by George III?

One thing the Brits do have over us: their vacations. A worker averages about a month a year of vacation.

Of course, it would never work here — especially not in Washington. Think of the anxiety. Oh the fear of being left out, losing your job or just being bored. Americans on long vacations get surly, marriages creak and desperate couples hunch over lunch in faraway places, trying to decide where to have dinner.

No. No. No. Our special genius has been the creation of the long weekend. We have more of them than most countries; they are envied even by the French who talk about — I kid you not again — le long weekend.

We have something here. Instead of pining for more vacation , we should build on the Fourth of July, Labor Day and Memorial Day by working only a four-day week.

I don’t like to point fingers, but there are those in the bureaucracy who are pioneering the new order for us. Around Washington, in the aisles of the supermarket and the sporting-goods emporium, you can hear it every Friday: Some person of impeccable rectitude about other things, declaring, “I’m working from my home office today.”

At the commuter rail station I use, parking is a big problem every day of the week except Fridays, when more than half the spaces are open. Well, not casting aspersions, I have to advise that 80 percent of the riders are government employees. Ah, the lure of the “home office” on Friday.

Here’s my proposal: Increase the workday to 10 hours and have three-day weekends every week. Once again America will be the envy of the world, even if we have to prohibit home-office work by civil servants on Thursdays. This way we’ll be a happier people. We’ll have given ourselves a present that keeps on giving.

Happy Birthday, America. And spare a kind thought for the Brits, who lost the best piece of real estate on Earth. Poor dears. — For the Hearst-New York Times Syndicate