BOOK REVIEW / MEMOIRS : A Transcendent Experience in Vietnam : THE MARK: A War Correspondent’s Memoir of Vietnam and Cambodia <i> by Jacques Leslie</i> , Four Walls Eight Windows, $22, 305 pages

In the second act of “West Side Story,” the musical, there’s a scene that the audience weeps at. Down go the lights with the smoke-colored gels and up come the lights with the pink-colored ones, and in their warmth the streets of Manhattan--the killing grounds for the Jets and Sharks--become what they hopefully could be. Graffiti and garbage disappear, the wilting clothes on the lines become banners, the skeletal fire escapes are stairways to paradise, and the two lovers sing, “Peace and quiet and open air, hold my hand and we’re halfway there. . . .”

That same sort of transcendent experience, drenched in sunshine and bonhomie, seems to have happened to Jacques Leslie in 1973, his second year in Vietnam, and he writes about it with infectious awe in the central chapter of “The Mark.”

Until then, Leslie, at 24 a war correspondent for the Los Angeles Times, had been like a Dante prowling Saigon’s mean streets. A prostitute in that inferno croaks at Leslie, “Hey you, GI, you come see me”; a deaf-mute prostitute uses unambiguous gestures; and a Vietnamese general / lunatic sits at a sidewalk bar, singing and screaming. The city, says Leslie, was like something painted by Hieronymus Bosch, and even more depraved was the Vietnamese countryside where the North and South held their inconclusive rumbles, where, near the bloated corpses, the Vietnamese marines sat playing harmonicas.

And then one day, Leslie did what no other correspondent had had the moxie (or the imagination) to do: He drove south of Saigon, parked, waded into a muddy paddy, walked on a bamboo bridge and took a farmer’s sampan into the VC territory. “People [were] waving Viet Cong flags,” writes Leslie with what Rene Descartes called the first of the passions: wonder. “The sun indeed shone here, seemingly more brightly than in Saigon. The people displayed more warmth than I’d seen in 13 months. . . .”

Now, please understand. Leslie wasn’t a pinko, peacenik, a person who thought, “I have seen the future.” He thought, as other reporters would, what a great story this was! Had anyone beaten him to it? Would he get a Pulitzer for it? Would the Vietnamese version of Western Union cable it to The Times? Would The Times even print it? (It would indeed: on the front page, six columns wide, above the paper’s own name.)

Leslie was simply an honest reporter on a beat where the truth often sounded like VC propaganda.

The VC shouted to Leslie, “Welcome!” They fed him hot tea, iced tea, hot coconut milk, chicken, steak, cookies and candy, saying, “You must eat plenty, so you can run from the shellings.” They invited him to a celebration and, in the dark of night, the shells started landing (they were the usual hit-or-miss) and Leslie dove into a ditch headfirst. The VC told him not to worry: The explosions were 200 yards away.

That night Leslie had sauntered (as Leslie calls it) onto the only meaningful story to come from the Vietnam War, for all the others were journalism of the absurd. For years the GIs had muttered that the Vietnamese were farmers by day; and Charlies--VC--by night, that the GIs couldn’t win unless they put all the Vietnamese on barges in the China Sea, then atom-bombed all of Vietnam, and then sank the barges too. And now Leslie looked at Vietnam from the inside out, from the bottom up, and lo! the GIs were right.

Since then, the passing years have validated much of what Leslie wrote.

The VC who told him, “We are friends,” are acting like friends indeed, even in My Lai and certainly more than our trading partners in Japan and China and France. The former forces of evil now have an office on R Street in Washington and recently when we asked them for $208.5-million damages (that’s right: We asked them) they nodded and promised to pay every penny. The questions that Leslie doesn’t ask and, if he did, couldn’t answer are: What were we scared of? What were we fighting for?

Leslie’s incursion into the land of coconut milk and cookies fills only 20 pages of “The Mark,” but his insightful reporting and evocative writing informs it all. He doesn’t just tell us yesterday’s news, for he often confesses to his own mixed motivations (and to his deviations in pot, opium and prostitutes) and the inadequacies of his fellow correspondents. Try though they might to be fiber-optic cables carrying the truth to America, their predilections and blind spots often impeded them.

The “mark” of the title identifies people, like Leslie, who felt most alive in the wild unpredictability (Will I be killed? Will I win a Pulitzer Prize?) and the resultant adrenaline rushes of Vietnam. On his first day there, a voice in Leslie whispered, “You are about to begin your real life. Everything from now on will be dramatic, romantic, intense.” His search for the source of this reputed neurosis didn’t really intrigue me, since everyone knows that a man who’s not yet a KIA is more alive in a war zone than anywhere in the United States.