The discovery of the battered bodies of five homeless men in six weeks has Denver police investigating whether the rash of slayings is the work of a serial killer preying on the homeless.

Among the city's estimated 5,800 homeless and those who wish to help them, fear is rising. Shelters are increasing foot patrols, searching abandoned warehouses and freeway underpasses in the hopes of coaxing the vulnerable and sick to safe houses.

Last Friday, an anonymous donor offered $100,000 for information leading to the capture and conviction of the killer or killers--the largest reward ever offered here to solve a crime. Mayor Wellington Webb, calling the murders a public safety crisis and using emergency powers, ordered the city's shelters to add more beds to get the homeless off the streets at night.

The police, who faced a similar situation three years ago when three homeless men were killed in a month and a half, have assigned seven homicide detectives to the case, which has been given high priority. FBI assistance has also been sought.

Homeless advocates have long maintained that those who sleep in the rough in American cities are the most victimized by crime and violence. Those crimes often go unreported and, they say, are frequently given short shrift by police. But officials here are taking the killings seriously.

"In Denver, whether one is living in a shelter or one is living in a palatial home, life is important," said Webb at a news conference Friday, flanked by police officials and homeless advocates. "It is critical that we find out who murdered these individuals."

The city's 1,300 shelter beds are almost always full and, with news of the slayings reaching even the most reclusive transients, the shelters are bursting.

"The word of mouth on the street is incredible," said the Rev. Del Maxfield, president of the Denver Rescue Mission. His outreach staff has been bringing in an additional 60 men per night to the 110-bed shelter. "The fear factor out there is very high. The guys are starting to realize this is not a random thing."

Police have little information on the five slayings, which they are treating as separate cases. According to Capt. Tim Leary, the men were savagely beaten, some with weapons and some with fists and feet. Leary said that while there are similarities among the attacks, "they are distinctly dissimilar in some respects," but he would not elaborate.

Police acknowledge the possibility that a serial killer may be preying on the homeless but said it is also possible that one person killed some of the men and a copycat carried out the other slayings. Only one case had witnesses.

In the same time frame of the slayings--since the beginning of September--authorities also have investigated four "serious" assaults against homeless men, they said Friday.

Authorities offered no motive for the killings of the men, who were described as having been outside the system and physically frail. According to Maxfield, two of the men were known at the Denver Rescue Mission. Donald Dryer and Milo Harris, both 51, were "really down-and-out guys, really hurting," Maxfield said. "They were physically weak and feeble. Looks like someone is picking on the worst of the worst."

Police have identified the other victims as Kenneth Rapp, 42, George Billy Worth, 63, and Melvin Washington, 47.

"It's hard for me to imagine what might motivate this," said John Parvensky, president of the Colorado Coalition for the Homeless.

Denver's homeless population has been displaced in recent years as downtown development, lofts and retail shops reclaim rundown warehouses and rail yards. More and more, homeless camps are springing up along the Platte River, which runs along the western edge of LoDo, the newly gentrified area of lower downtown.

LoDo is a busy neighborhood that is crowded day and night and includes Coors Field, restaurants and upscale shopping. The fact that the bodies were found in such a busy part of town makes the slayings seem all the more brazen.

Nationally, violence against the homeless has reached such a level that some advocates are calling for such attacks to be considered hate crimes. Statistics on violence against the homeless are hard to come by, but a 1994 study by the Coalition for the Homeless in New York found that 90 percent of the homeless people surveyed had property stolen and 80 percent had been victims of violent crimes. An updated survey is being prepared.