A lethal disease that wipes out the body's natural defense system has topped 1,000 cases, causing 394 deaths, and the pace appears to be accelerating, with about 20 percent of the cases reported in the last two months.

The Acquired Immune Deficiency Syndrome (AIDS) outbreak is "of grave concern," said Dr. William Foege, head of the Centers for Disease Control. "This is a major public health problem."

A government task force led by the CDC is completing the controversial task of developing new guidelines to help prevent the spread of AIDS, particularly through blood donations. The most difficult task is how to reduce donations from groups considered at high risk of contracting AIDS, including male homosexuals, intravenous drug users and Haitians.

This is compounded by the limited evidence as to what causes [AIDS] and how it spreads. To date, nine hemophiliacs have contracted AIDS after receiving a blood concentrate created from a pool of many donors and designed to prevent bleeding. The National Hemophilia Foundation wants blood banks to screen out high-risk groups, an approach that has been denounced by the National Gay Task Force.

Foege said his concerns were:

* The rising incidence. As of Feb. 2, cases totaled 1,025. January was the worst month since the CDC learned of the disease in 1981. "My judgment is that there is a true increase in the incidence of the disease," Foege said.

* The mortality rate. About 40 percent of the victims have died of AIDS, but it appears to be far more lethal. Of cases diagnosed a year ago, more than 60 percent have died and the toll may go far higher.

* The growing number of risk groups. Although AIDS was first detected in some homosexuals, it has since been found in intravenous drug users, some of their sexual partners, Haitians, hemophiliacs, other blood transfusion recipients and children.

The failure to find a cause. Although there is growing agreement that an infectious agent may be at fault, none has been found. In fact, there is no definitive test for diagnosing AIDS.

* The magnitude. "We don't know whether we're seeing the top part of this disease. Our suspicion is its the tip of the iceberg," Foege said. The lag time between infection and disease may be a year or longer.

"The cases are still relatively restricted geographically and by risk group. It's likely to continue to increase further," said Dr. James Curran, head of CDC's AIDS team.

While cases have been reported from 33 states, there is still a concentration in New York, 49 percent, and California, 22 percent. CDC lists only 17 cases from the District, Maryland and Virginia. Nearly three-fourths of the victims are homosexuals, followed by drug users, 16 percent, and Haitians, 5 percent. One of the most troubling questions is the degree of risk in blood products. At the moment, debate is focused on the effort to develop guidelines for preventing contamination of blood products, given the limited state of knowledge.

CDC's Dr. Harold Jaffe said the nine hemophiliacs contracted AIDS after receiving factor VIII blood concentrate. The CDC is also investigating "eight cases who don't fit known risk groups and received blood within several years of the onset of illness," he said.

For the general public, Jaffe said, the risk of contracting AIDS from a blood transfusion seems to be "very small" but could increase in the future.

Homosexual groups argue that the blood policy proposals for excluding high-risk groups unfairly single out gay men. "We should screen blood not people," said Virginia Apuzzo of the National Gay Task Force.

Her group is pushing for the use of "surrogate" or marker tests that would help identify those at risk. Surveys have shown that nearly 90 percent of AIDS victims are also positive in antibody tests for hepatitis B.

Blood bank organizations worry about the practicality and cost of such testing. The American Association of Blood Banks, the American Red Cross and the Council of Community Blood Centers have recommended additional steps to expand donor screening to detect possible AIDS symptoms or exposure to patients with AIDS. They concluded, however, that specific questions about "sexual preference were inappropriate and ineffective."

The government's task force, drawn from the CDC, the National Institutes of Health and the Food and Drug Administration, is completing its guidelines.

According to sources, there is an emerging consensus that the guidelines suggest high-risk donors voluntarily refrain from donating blood. Such donors would include sexually active homosexual men, drug users and Haitians.

But health officials are particularly sensitive about stigmatizing these groups, and seem to be steering away from the National Hemophiliac Foundation's recommendation. Sources suggested that potential blood donors might be informed of the AIDS concerns but not excluded by specific questions. The sources indicated that the need for feasibility testing of "surrogate" blood tests would be considered, but a blanket recommendation for routine use was unlikely.

Preventive guidelines, such as the recommendation that gay men limit the number of sexual partners, may be included, the sources said.

Spokesmen said that a final recommendation is expected to be submitted to Health and Human Services Assistant Secretary Edward Brandt Jr. this week and that he could make a decision within two weeks.