In an effort to get blacks to take to heart the risk of AIDS, Metrobus billboards in Washington will soon bear a frightening and blunt message.

Over a picture of black men and women, the public service advertisement will bear a warning: "Every two hours, a black American dies of AIDS. Don't be next in line."

The billboards, which will appear before Dec. 1, reflect an escalation in the District's public education campaign and a realization that, judging by statistics showing a disproportionate number of black people nationally with AIDS, blacks need to hear more and in stronger terms about the spread of the deadly virus.

In recent months, public health officials and church leaders have expressed concern that the message about AIDS appeared not to be taking hold among blacks. The ad campaign is a first step toward the more penetrating, audience-capturing messages that the D.C. Public Health Commission plans to use, Commissioner Reed V. Tuckson said.

But some who heard of the latest District campaign fear that it may be too negative to have the desired impact, and that it carries an implicit -- some say racist -- message of doom.

"I guess I feel about that the same way I felt about the cancer ads that went out a few years ago," said Dr. Cheryl Sanders, an assistant professor of Christian ethics at the Howard University Divinity School, referring to American Cancer Society ads three years ago that warned black Washingtonians of a high risk of cancer. "I'm glad for the concern for public awareness, but I do have some reservations about putting the message in those terms . . . . It may be that the negative approach will frighten people more than inform them."

The Rev. Ernest Gibson, pastor of First Rising Mount Zion Baptist Church, said the negative message, however, should not obscure the reality that blacks are being affected by acquired immune deficiency syndrome. "The reality is that more blacks are dying," he said. "It is blunt, but it is true."

Responding to reservations that some have expressed about the ad campaign, Tuckson said that the need for AIDS education supersedes whatever criticism the new ad may receive.

"The facts are the facts, and if we do not let people know that they are at risk, at very real risk, then we would have failed in our responsibility," Tuckson said.

According to statistics compiled by the federal Centers for Disease Control in Atlanta, blacks, who make up 12 percent of the nation's population, account for 25 percent of its AIDS cases. In the District, where blacks are 70 percent of the population, they account for 50 percent of the city's AIDS cases.

Still, officials say, a perception exists in the District that white homosexual men have been hardest hit by the virus, and many blacks have viewed AIDS education campaigns with detachment.

The AIDS virus is transmitted mainly through an exchange of blood products or body fluids in sexual intercourse, blood transfusions, or intravenous injections using contaminated needles, medical authorities say.

The CDC projects that by the end of December the nationwide AIDS death toll for the year will be 16,800, and 4,200 of those deaths will occur among blacks. Calculate that down to hours, and the statistics can be interpreted to mean an AIDS death rate among blacks of one every two hours, said Dr. Meade Morgan, chief of the CDC's AIDS program statistics branch, which made the nationwide hourly breakdown.

There is no such hourly death rate breakdown for the District.

Judy Walton, AIDS project manager for Spectrum, a black health organization that developed the latest public service ads under contract with the city, said they represent a stepped-up campaign to urge blacks to take preventive measures. Preliminary tests of the ad's effect showed that "it was really getting people's attention," she said.

"I consider it to be an ad, I guess, frightening in a sense. People sort of stop when they read it," Walton said. But the message, she said, is intended to say, "Yes, you may be at risk and there's things that you need to do."

That message also is being disseminated by black church leaders, who have been meeting to share information and develop strategies to educate their congregations about the deadly virus.

The morality of homosexuality and promiscuous sex, Gibson said, are no longer prohibiting some church leaders from speaking out about AIDS. "I think most pastors are moving beyond that now and are ready to give a loving and compassionate service" to people suffering from AIDS.

Tuckson, however, said that judging by the behavior of some, the message is far from perfected.

"Unfortunately, there are still far too many persons in this city who do not think that they need to change their behavior, and who, even though they have information, do not act upon it in a responsible way, for themselves and for others," he said.