A black Citroen sedan rolls slowly along wide, brightlighted Thong Nhut Boulevard in Saigon, carrying a thin Vietnamese man named Nguyen Van Muoi. In the back seat he had his personal talisman - an ornately decorated samurai sword. It is shortly after 2:30 a.m. on January 31 - the first night of the Vietnamese new-year holiday - and Saigon's three million are asleep after daylong celebrations. A so-called truce is on; nearly half the government troops in all the country are away from their posts on leave.

Muoi drives slowly past the smartest new building in Saigon, a great white material statement, the $2.6-million U.S. Embassy, dedicated just four months ago, built as a fortress, with reinforced-concrete compound walls, shatter-proof Plexiglas windows, a terra cotta sun screen that acts as a bomb shield over the whole structure, and a copter pad on the roof of its penthouse. Along the boulevard, Muoi turns, approaches the building again, looks at his watch, shouts from the car window.

Nineteen young men of the Viet Cong's select C-10 Sapper Battalion, some in black farm pajamas with red armbands, some in green jungle suits, all armed with Chinese AK-47 submachine guns and carrying among them three 3.5-inch rocket launchers, dash from hiding places. They shoot down two U.S. military policemen on guard at the side gate on Mac Dinh Chi Street. At 2:54 a.m., with rockets from the powerful bazookas, they blow a hole in the compound wall, and a couple scramble through.The Embassy's night duty chauffeur, Nguyen Thai Ba, unarmed, impulsively rushes the intruders; they kill him. They shoot the lock off the side gate and let their comrades in. The men take up planned stations in the four-acre compound . . .

Six hours later - but not before cameras had caught glimpses, for all incredulous America to see, of this fanatically courageous penetration to the very heart of U.S. complacency in Vietnam - Marines from the 716th Police Battalion, two helicopter-borne platoons of "Screaming Eagle" paratroopers from the 10st Airborne Division, and mission coordinator Colonal George Jacobsen, singlehanded, armed with a pistol thrown up to him in a window, had killed all nineteen of the terrorists, whose bodies lay blood-soaked among the ornamental flower pots along the compound's gravel walks.

In those same morning hours of the first night of Tet, 84,000 men of the National Liberation Front - which for months General Westmoreland and Ambassador Ellsworth Bunker and Deputy Ambassador Robert Komer had been charaterizing as exhausted, played out, at the end of their rope - attacked five of six major cities, 36 of 40 provincial capitals and 64 district capitals, and nearly every American base in Vietnam. Eleven NLF battalions entered Saigon, penetrating the grounds of the presidential palace, capturing the government radio station, overrunning Tan Son Nhut air base. The most "secure" of the provincial capitals in the Mekong Delta - Can Tho, My Tho, Vinh Long, Rach Gia, Ben Tre - were all broken into; and in the mid-flank of Allied operations the NLF attacked Nha Trang, Qui Nhon, Tuy Hoa, the resort town for South Vietnamese generals at Dalat, and the major American base at Cam Ranh Bay. The most vicious attacks of all were in the north, where North Vietnamese forces joined in, shutting down the hugh American air base at Da Nang for a time, hitting other American bases at Chu Lai and Phu Bai, and in Hue driving to the center of the city, taking over the provincial headquarters, the university, the market, and the imperial citadel.

Within days of the first assaults, General Westmoreland called the Tet offensive "a go-for-broke proposition" and a costly failure for the enemy. Toward the end of the first week, the U.S. command announced a body count of 14,997 enemy soldiers, while, it said, 367 U.S. and 738 South Vietnamese had been killed. These body counts were getting hard to believe; it had begun to seem that Viet Cong by the thousands were rising from the dead. The fighting dragged gruesomely on. Hue was not cleared of the enemy until February 24, and then 7,000 of its 17,000 houses were in ruins and there was a look of hallucination in the eyes of the Americans grunts who had survived there. After Tet, 670,000 South Vietnamese were said to be homeless.

When the offensive was finally over, Westmoreland claimed a major victory - and knocked the pins out from under the claim by asking for 206,000 additional troops and more air squadrons. In a sense the Allies had won the round. The NLF had not succeeded in rallying the population to its side; the Front had suffered hard losses; the government had not fallen.

But the American people now knew - though they might not yet admit they knew - something General Westmoreland did not know. Vietnam was a lost war. The United States had never lost a war. They were going to lose this one.

What forced this admission - a thousand times more humiliating than the Pueblo affair - to come near the surface were, above all else, those images of the enemy in the Saigon compound, causing death and consternation in the very seat of American power. There was no explaining away the photograph of the U.S. official defending himself with a handgun in an Embassy window.

At an even deeper level, after Tet, Americans who had previously supported the war suffered their first dim realization that we were harming by "helping" the South Vietnamese - doing harm beyond redress, and harm that hurt us, too, and right where it mattered; in the Dream. All of Vietnam was summed up by the American officer who, after Tet, said to the Associated Press correspondent as they surveyed the ruins of the town of Ben Tre, "We had to destroy it in order to save it."

Nixon announces his candidacy . . . A week later Wallace jumps in . . . At the Judson Poets' Theater in Manhattan, three men and three women dance and sing The Sayings of Mao Tse-tung, and a critic of the Village Voice writes, "The performers are peppy and full of personality." . . . Peggy Fleming, the figure skater, wins the only U.S. gold medal at the winter Olympics . . . Draft deferments are abolished for graduate students . . . In a "grass ballot" of the audience of San Francisco's rock - and - roll station KMPX, Bob Dylan ("Blowin' in the Wind," "Times They Are A-Changing," "Don't follow leaders, watch your parking meters," "Dear Landlord, please don't put a price on my soul," "You don't need a weatherman . . .") is elected next President of the United States . . . Hundreds of thousands of tons of garbage pile up in the streets of New York as collectors go on strike . . . Another delegation of 33 SDSers, including a Columbia sophomore named Mark Rudd, goes to Cuba . . . Romney withdraws . . .