When I entered active duty in July 1961 as a second lieutenant in the U.S. Army, there were about 2,000 U.S. military advisers in Vietnam. During my two years of service, Washington's attention was primarily focused elsewhere: on the Cold War in Europe and on Berlin, where communists built the wall in August '61; and on Cuba, where John F. Kennedy ordered a naval blockade during the 1962 missile crisis that took us closer to war than many imagined at the time.

When I left active service in 1963, Americans in uniform were still being sent to Vietnam as advisers, although the military assistance group had grown to about 15,000.

John Kerry entered active duty at a different time. It was 1968, and Vietnam was on everybody's lips back home -- that is, when people weren't busy watching explosions on the home front.

That year, when Kerry was on the guided-missile frigate USS Gridley and then ordered to Coastal Squadron One, Coastal Division 14, Cam Ranh Bay, in South Vietnam, the Tet offensive was launched; the My Lai massacre was uncovered; President Lyndon Johnson, hounded by the war, announced he would not seek reelection; Martin Luther King was assassinated and U.S. cities went up in flames; Robert F. Kennedy was shot and killed after winning the California Democratic primary; the Democratic convention was roiled by demonstrations in the streets; and U.S. troop strength in Vietnam reached 540,000.

More than 58,000 Americans died in that war. Of those killed, 25,481 were between 18 and 20 years old. Everyone who went to Vietnam, volunteer or draftee, enlisted service member or commissioned officer, combatant or noncombatant, Democratic presidential hopeful John F. Kerry or author John E. O'Neill, is a hero in my book.

End of story.

But not for the authors of "Unfit for Command," the book by O'Neill and Jerome R. Corsi that makes the anti-Kerry TV ads by the Swift Boat Veterans for Truth look like mosquito bites. From the book's introduction through more than 200 pages, Kerry is hammered, kicked, punched and kneed. The authors hate him.

To them, Kerry is a liar, a fraud and the recipient of undeserved medals. They accuse him of using fake awards as a basis for seeking the presidency. He's denounced as a cheat whose conduct represents "unbelievable hypocrisy and the truly bottom rung of human conduct." And that gets us to about Page 31.

Much of their censure of "war hero" Kerry is, by now, familiar. He's depicted as a hunter of Purple Hearts who used two self-inflicted wounds and a fabricated wound to "game the system" and win early passage out of Vietnam -- "a one-year tour completed in the record time of four months," as the authors put it. They charge that Kerry's Silver Star and Bronze Star were awarded based on false information. And they claim to back up their accounts of Kerry's non-derring-do behavior in Vietnam with stories from anti-Kerry veterans who served with him.

"Unfit for Command" has become a bestseller. But readers ought to know there are point-by-point rebuttals of anti-Kerry accusations by other veterans who served under and beside him. The book's authors don't give Kerry's supporters the space or the credence that they warrant. To get the other side, readers have to go to investigative accounts in The Post and other major newspapers. And there's also Kerry's Web site (www.johnkerry.com)

What's more, the authors of "Unfit for Command" should have, in the interest of full disclosure, revealed their own connections with the Bush campaign as well as the sources of their financial support. They didn't. Those items of interest are also available in stories that appeared in The Post, the New York Times and the Los Angeles Times.

But "Unfit for Command" is not really about John Kerry, the naval officer. The book is aimed at John Kerry, the antiwar protester and spokesman for Vietnam Veterans Against the War. And this is where "Unfit for Command" really gets mean. It calls into question Kerry's loyalty. The Kerry camp cannot let this kind of smear stand.

Kerry's April 22, 1971, appearance before the Senate Foreign Relations Committee, during which he gave a firsthand criticism of the war and reported graphic and shocking stories about the behavior of other Americans in Vietnam, is what set off O'Neill and other Swift boat veterans. They claim that Kerry's testimony was a slap in their faces as they were, at the moment he appeared before the committee, fighting and dying in Vietnam. Plus, they say, Kerry failed to provide proof or documentation to back up his charges of atrocities having been committed in the normal course of duty. They believed Kerry had falsely painted them all as criminals.

The book, however, doesn't leave it at that. "Unfit for Command" takes a swan dive into McCarthyism, choosing to paint Kerry's testimony to the committee -- "whether he knew it or not" -- as "reciting the Communist Party line chapter and verse." They cite Soviet KGB defector Ion Mihai Pacepa, who was quoted as saying that Kerry's 1971 war crimes accusations sounded to him just "like the disinformation line that the Soviets were sowing worldwide throughout the Vietnam era."

The book also charges Kerry with:

* "Meeting with the enemy in Paris and coordinating ongoing meetings with various members of the [Vietnam Veterans Against the War], both in Paris and Hanoi, to arrange the release of American POWs to the VVAW. [They say elsewhere in the book that the meetings were designed to enhance the VVAW's status and advance the antiwar movement by having the prisoners released to the VVAW.] These meetings also provided aid and support to the North Vietnamese Communists in the form of radio broadcasts and other indoctrination methods aimed at encouraging U.S. soldiers in the field to lay down their arms and desert the military."

* "Giving a press conference in Washington, D.C., in which he advocated a Vietnamese Communist peace proposal that would have called for a complete withdrawal of the United States military and an abandonment of the government of South Vietnam, in other words, a surrender on enemy terms, followed by the payment of war damage reparations by the United States to the Vietnam Communists."

Kerry can and should discuss his antiwar record. Many of us ended up opposing the Vietnam War; there is no shame in that.

John Kerry's record is officially documented by the Defense Department. John Kerry's tour in Vietnam is also recorded in the minds of those who served with him. So are his antiwar activities. Some remember him well. Some do not.

Speaking for myself, it is enough that he served.