A middle-aged woman walks along the sidewalk with her left hand to her forehead and her face in a grimace of intense pain. To her right, flatbed trucks crammed with young people carrying Czech flags roll along the cobblestone street. The young people overflow the trucks, sitting on the roofs of the cabs, the hoods, and the fenders. A woman seen in profile stands at the curb watching them apprehensively and scratching her chin. The sky is overcast. The photograph is grainy. It is one of the first of more than 150 black-and-white pictures on display at the Aperture Gallery in Josef Koudelka’s “Invasion 68 Prague,” a selection of the Magnum photographer’s epic record of the Soviet-led occupation of his homeland 40 years ago.

Succeeding images of tanks in flames, of armed and helmeted soldiers, of dead civilians, and of efforts at resistance suggest that the pictures are combat photography, but really another aesthetic is at work here, namely street photography. Russia and its Warsaw Pact allies invaded Czechoslovakia on Tuesday, August 20, 1968, to remove the government of Alexander Dubcek, whose liberal policies were a challenge to the totalitarian rule of the Soviet bloc. For a week, the invaders faced the citizens of Prague in a confrontation many expected to end in a massacre. Mr. Koudelka, then 30 years old, was in the streets continuously, taking thousands of pictures at great hazard to his safety. He shot with an Exakta, one of the first successful 35mm single-lens reflex cameras, which allowed him to quickly compose, shoot, and move on. Although he had a 180 mm telephoto lens, one a combat photographer might be expected to use, it saw little service. Instead, he relied on his 25 mm and 35 mm wide-angle lenses, the favorites of street photographers. These lenses are ideal for shooting in restricted urban spaces; they have great depth of field, so that focusing is not critical and, most important, the pictures they produce have a sense of intimacy.

There is intimacy in the concentrated faces of a mass of protesting citizens — men and women, mostly young — which is presented in a 36.5-by-24-inch format at Aperture, and as an enormous 233-by-104.25-inch mural at a simultaneous exhibition of Mr. Koudelka’s work at the Pace/MacGill Gallery. There is intimacy in the portrait of a tank aiming at the Czechoslovak Press Agency building in Wenceslas Square, with the camera virtually pointed down the muzzle of the tank’s cannon. And in the picture of a young man gesturing imploringly to Soviet troops sitting on a tank at the Czechoslovak Radio building on Vinohradská Avenue, framed so that the Russians’ boots take up much of the lower right quarter of the image. In the wrinkled brow of the old man standing in front of a bullet-ridden and burnt-out building also on Vinohradská Avenue. In the anxiety betrayed in the face of a Soviet soldier holding an automatic rifle as he confronts a civilian, smoky fires burning on the street in the background. And there is intimacy in the picture of two dead victims of the fighting at the Czechoslovak Radio building. One lies face downward, and all we see of him is his lifeless hand; the other lies on his back so that we see his sorrowful face, with blood coming out of his mouth, and the Czech flag he carried to his death lying on his chest.

Mr. Koudelka left his job as an aeronautical engineer to pursue photography full-time only in 1967, but for several years he had been photographing gypsies — a despised group in the regimented Soviet bloc — and the Theater Beyond the Gate drama troupe. The latter group taught him “to see the world as theater,” training he put to good use in that August of ’68. There are pictures of great theatricality, almost like movie stills. Four sad-eyed men arrayed in various planes bid farewell to the martyred dead. Two young men cross a rubble-strewn street holding up a Czech flag and gesturing to the crowd. A pack of Soviet soldiers sits isolated atop a tank surrounded by a sea of Czech civilians pressing in on them. And most memorably, a man brandishing a Czech flag stands astride a Soviet tank on a street lined with watching men, while sm ground from multiple fires. This is the image Aperture has made into a mural, 148 by 98 inches, and placed in the center of the “Invasion 68 Prague” exhibition.

Mr. Koudelka’s photos from that traumatic week were smuggled out of Czechoslovakia, and made their way to Elliott Erwitt, a former president of Magnum Photos, who saw that they got published in 1969 on the anniversary of the invasion. They were credited to an “anonymous Czech photographer,” and that year the “anonymous Czech photographer” was awarded the Robert Capa Gold Medal by the Overseas Press Club. It was 16 years before Mr. Koudelka could acknowledge he was the photographer without jeopardizing his family. Now, on the 40th anniversary of the invasion, a book with 250 of the pictures — also titled “Invasion 68 Prague” — is being published in nine editions, and in as many languages. It will be a useful reminder to a forgetful world of what the Cold War was about, and the importance of American resolve in the face of what seemed inevitable Soviet hegemony.

I asked a Magnum representative at Aperture which were the nine languages the book was published in. He ticked them off, and I asked, “But not Russian?” He said no; they tried to find a Russian publisher, but none had the courage. With Russian troops now in Georgia, of course not.

wmmeyers@verizon.net

“Invasion 68 Prague” at the Aperture Gallery, September 5 through October 30 (547 W. 27th St., 4th floor, between Tenth and Eleventh avenues, 212-505-555).

“Josef Koudelka: Invasion 68 Prague” at the Pace/MacGill Gallery through October 11 (32 E. 57th St., 9th floor, between Madison and Park avenues, 212-759-7999).