No beards or other "Islamic characteristics." Do not speak loudly or otherwise draw attention to yourself. Rent apartments in areas where neighbors do not know each other well.

The suicide hijackers in last week's attacks apparently practiced terrorism by the book — a 180-page manual for Muslim operatives living undercover among their enemies in "godless areas" of the world.

The manual, "Military Studies in the Jihad Against the Tyrants," was discovered last year during an investigation of Usama bin Laden, and gives terrorists precise instructions on how to act while they await their orders to strike.

Investigators have not said whether the 19 hijackers ever read the manual, but glimpses of their lives suggest they conducted themselves according to its instructions during the months they spent in the United States.

Experts say the manual illustrates the inner workings of bin Laden's al Qaida organization, the prime suspect in the attacks. It also foreshadows the suicide hijackings themselves, in which the terrorists used boxcutters and knives.

For example, the manual's "Assassinations" section gives precise instructions on how to use weapons with blades, saying the "enemy must be struck in one of these lethal spots: Anywhere in the rib cage, both or one eye, the back of the head, the end of the spinal column."

The hijackers "seem to have followed [the manual] as closely as they could ... making sure no one knew the whole picture," said George Andrew, former deputy head of anti-terrorism for the FBI's New York City office.

The manual says anyone willing to "undergo martyrdom" should be "able to act, pretend and mask himself" behind enemy lines.

Among its instructions:

• Do not address others with traditional Islamic greetings in which Allah's name is invoked.

• Do not cause trouble in your neighborhood. Do not park in no-parking zones.

• Do not live near police stations.

• Do not appear to be overly inquisitive.

• Burn letters immediately after reading them, and get rid of the ashes, too.

• Rent apartments "in newly developed areas where people don't know each other."

• Use codes when talking on the telephone.

• Try not to be "chatty and talkative" in public.

• Maintain an appearance "that does not indicate Islamic orientation (beard, toothpick, book, long shirt, small Koran)."

Most television images of the men thought to have been aboard the airliners show them without beards. And people who met them said they wore Western clothes.

Neighbors of some of the men in California, Florida and Maryland said they lived in suburbs where they did not stand out. In Florida they moved frequently, staying in motels and apartments around the state.

They also joined gyms. One made small talk with a neighbor about sports; another posted a personal ad on the Internet.

People who came into contact with them described them as quiet, friendly and sometimes timid men who gave few, if any, hints that they harbored deep resentment against the United States.

Nawaq Alhamzi, a suspected hijacker aboard the jet that crashed into the Pentagon, lived last fall in a new 175-unit San Diego apartment building where so many people came and went that he was barely noticed. He always paid the rent on time.

Some of the hijackers appeared to bend a rule in the manual stating that "there is nothing that permits ... drinking wine or fornicating."

Days before the World Trade Center attack, Mohamed Atta and Marwan Al-Shehhi were seen drinking at a sports bar in Hollywood, Fla. Majed Moqued was spotted perusing adult videos in two Laurel, Md., stores. He did not buy anything.

FBI agents discovered the manual last year in Manchester, England, in one of several "guest houses" authorities say al Qaida used to harbor terrorist cells. The FBI was investigating bin Laden and his suspected role in the deadly 1998 bombings of two U.S. embassies in Africa.

After studying the manual, the FBI suspected that bin Laden's soldiers were attempting to infiltrate American society, said Andrew, the former FBI anti-terrorism official. But investigators apparently did not conclude that terrorists had already put themselves in position to strike.

They "didn't think they were at that chapter yet," Andrew said.