They swooped in after the Oklahoma City bombing in 1995, the crash of TWA Flight 800 a year later and the killings at Colorado's Columbine High School in 1999.

Now proponents of a controversial and increasingly popular treatment for post-traumatic stress disorder (PTSD) called Eye Movement Desensitization and Reprocessing, or EMDR, are offering free therapy sessions to the latest group of traumatized Americans: survivors of the Sept. 11 attacks at the Pentagon and World Trade Center, relatives of those who were killed and workers involved in the ghastly rescue and recovery efforts.

Officials at the EMDR Disaster Response Network have begun calling local police and fire departments as well as companies' and government agencies' employee assistance programs to offer the services of 50 therapists who have agreed to provide four free, 90-minute sessions to those directly involved in the attacks who may be showing signs of stress-related psychiatric problems. The group is also advertising its pro bono services on a Web site and is preparing to launch a media campaign.

"We're just starting to get calls" in response to these offers, said Washington psychologist Jeanette Paroly, president of the EMDR Humanitarian Assistance Program, which oversees a 500-member national network of volunteer therapists and whose group has fielded recent inquiries from the Secret Service Employee Assistance Program and the U.S. Marshals Service.

"We're kind of a second wave response after the rescue workers leave," said Barbara Korzun, executive director of the program, which is based in New Hope, Pa. "The patients who've been finding us are the people who've heard about EMDR and have been unable to cope."

EMDR combines a standard behavioral technique called exposure -- in which a patient confronts a traumatic memory in a supportive setting -- with a series of rapid eye movements which are supposed to metabolize and then reprocess troubling memories. For a Pentagon survivor, exposure therapy might involve conjuring up in vivid and disturbing detail the sound of the plane crash, the bloody face of a co-worker, the smell of sudden death. While orthodox exposure therapy may require a patient to remain focused on the image for a long time, EMDR allows a patient to essentially free associate and to think of other things during the 90 minute session; it also adds eye movements or sounds to the therapy.

Since 1989, EMDR officials say, more than 30,000 mental health workers have been trained at authorized commercial workshops and more than 2 million patients have been treated worldwide.

Although EMDR has attracted a growing number of enthusiastic adherents, it also has spawned an ardent group of critics who say the treatment amounts to aggressively marketed "pseudoscience." Detractors say claims that EMDR works faster than, or is superior to, standard exposure therapy or other established treatments for PTSD are unproven.

"I concur with the view that what's new about EMDR is not helpful and what's helpful is not new," said psychiatrist Robert J. Ursano, echoing a characterization by Harvard University psychology professor Richard J. McNally, the author of a 1999 article detailing the many similarities between EMDR and a discredited 18th century treatment called Mesmerism, which relied on the manipulation of a body fluid dubbed "animal magnetism."

Ursano, a nationally respected PTSD expert who chairs the Department of Psychiatry at the Uniformed Services University of the Health Sciences, the military medical school in Bethesda, added that "there's no neurobiological data that supports" EMDR.

"My own beef about EMDR is that the claims are outlandish," said Scott O. Lilienfeld, an associate professor of psychology at Emory University in Atlanta and an editor of a journal called The Skeptical Inquirer. "There is no evidence that it is novel or a breakthrough. It's been aggressively marketed as a very quick fix for a very intractable, hard-to-treat and frustrating psychological problem, and unfortunately a lot of clinicians are not very well trained scientifically and they latched onto it. It sounds really, really scientific."

But Deany Laliotis, the Washington-based coordinator of the EMDR Humanitarian Assistance Program, said she finds the arguments of academics unpersuasive. "All I can tell you is what I know and what I see in my office, which is that I've treated hundreds and hundreds of people over the last 10 years, and EMDR is much more efficacious and efficient than standard treatment," said Laliotis, who is a social worker. "It may be anecdotal, but I trust my experience."

EMDR therapy was introduced a dozen years ago by Francine Shapiro, a California psychologist who discovered the treatment while taking a walk in a park. Shapiro said she was thinking about her problems when she noticed that she felt better after her eyes darted back and forth rapidly, as if she was watching a fast tennis match.

She achieved similar results after trying the method on friends and colleagues, asking them to concentrate on a troubling thought while she flicked her fingers in front of their eyes. Shapiro then made EMDR the subject of her doctoral dissertation; she holds a PhD from the never-accredited and now defunct Professional School of Psychological Studies in San Diego. In 1989 Shapiro published a study of 22 patients in the peer-reviewed Journal of Traumatic Stress. EMDR was launched.

Several years ago Shapiro decided that rapid eye movements were not essential to EMDR and that the same effect could be achieved using tones or taps. Treatment is now sometimes accompanied by technology, including a $549 eye scanner operated by the therapist and sold on one of three official EMDR Web sites. The patient visualizes a traumatic memory while the therapist flicks two fingers -- or a lighted wand -- rapidly back and forth in front of the patient's eyes. These movements are repeated at least a dozen times during a 90-minute session.

"What you're doing is allowing a person's mind to go where it needs to go in their memory network to get better," Shapiro said in a recent interview. In the past she has said that the eye movements essentially dislodged troublesome memories and sent them to a different part of the brain where they were reprocessed and rendered more benign.

"Changes are going on in an emotional and intellectual and body level," Shapiro said. "What happens in EMDR is that you're catalyzing the learning process."

But a meta-analysis (a way of assessing results from multiple studies to draw a conclusion) of 34 EMDR studies conducted by Canadian psychiatrists P.R. Davidson and K.C. Parker of Queen's University in Kingston, Ontario, published last April in the Journal of Consulting and Clinical Psychology, found that while EMDR was superior to no treatment, it was no more effective than exposure techniques. The researchers also found that when EMDR was performed without eye movements, there was no difference in outcome -- "which suggests that the eye movements integral to the treatment, and to its name, are unnecessary."

"The eye movement is not the magic bullet," Shapiro said, noting that taps or tones were added after treatment performed on a blind client and an uncooperative child. "If you take out eye movements . . . you still can get positive effects."

The National Institute of Mental Health (NIMH) reports that a few treatments have demonstrated effectiveness in treating PTSD: EMDR is not among them. The treatments include exposure therapy and cognitive behavioral therapy, a short-term treatment in which a person is taught to logically think about and manage symptoms. Anti-anxiety medications and antidepressants have proven to be helpful as an adjunct to talk therapy, according to the NIMH. Conventional long-term psychotherapy rarely works for PTSD.

Psychiatrist Bessel A. van der Kolk, who directs the Trauma Center at the Boston University School of Medicine, said he believes EMDR is an effective treatment for PTSD -- and not because it relies on repeated exposure to a traumatic event. "I think most therapies require too much talking from people, and trauma is a nonverbal experience," he said. Van der Kolk, who has a grant from the NIMH to study EMDR, said that he's not sure precisely why it works, but hypothesizes that it "opens up alternate networks" in the brain.

Steven V. Marcus, a psychologist at Kaiser Permanente in Santa Clara, Calif., said he has performed EMDR since 1992. "How EMDR works is not clear, but neither is psychotherapy," he said.

"I think a lot of the critics are academics, not clinicians, and they haven't been properly trained to use EMDR," said Marcus, the author of a study that found that EMDR was superior to standard mental health treatment given at a Kaiser clinic. The study also found that the health maintenance organization could save $2.8 million by offering EMDR to all PTSD patients in Northern California. Kaiser currently offers EMDR in Northern California, Marcus said.

A major advantage of EMDR, proponents contend, is that it works much faster than other PTSD therapies. Training is open to those with a master's degree and a license.

The EMDR Humanitarian Assistance Program Web site, which advertises the free therapy for Sept. 11 survivors, says that "in as few as three sessions, trauma survivors can experience the benefits of psychotherapy that once took years to make a difference." Shapiro said that "study after study" has found that 90 percent of PTSD patients treated with EMDR are free of the disorder after three sessions.

But several studies suggest that the improvement patients report may be temporary. Psychiatrist Roger K. Pitman and a team at the Veterans Affairs Medical Center in Manchester, N.H., published a follow-up study of 13 Vietnam combat veterans with chronic PTSD who were treated with EMDR compared to a control group that received no treatment. While the EMDR group showed immediate improvement, five years later the symptoms of patients in both groups had worsened.

Ursano suggested that EMDR's successes can be explained by the patient-therapist relationship and the belief that treatment will work, a phenomenon known as the placebo effect. "Much of successful psychotherapy relies on the relationship with a therapist," Ursano said.

Emory's Lilienfeld noted that while there is no evidence that EMDR is harmful, that doesn't mean treatment is inherently risk-free. "If you mis-administer any treatment you can do a lot of harm," he said, "in this case by exposing people to an anxiety-provoking stimulus. And if you leave that anxiety at a very high level, the patient is going to get worse."

EMDR advocates' suggestion that their therapy is the treatment of choice for trauma bothers psychiatrist Liza H. Gold, an assistant professor of psychiatry at Georgetown University School of Medicine.

Gold said that while pro bono treatment "is a very generous idea," all patients should receive a thorough workup to rule out an underlying medical or other psychological problem. "I'm not sure the people who do EMDR are trained to do a comprehensive evaluation," said Gold, who practices in McLean and specializes in treating female trauma victims. "You can't just do one-size-fits-all-therapy."

But Laliotis, the Bethesda social worker, says she has successfully used EMDR for a host of difficulties, from improving a patient's golf score to helping a patient recover from a rape. EMDR, she said, "can be used for anything."

Bethesda social worker Deany Laliotis demonstrates the finger-waving technique used in EMDR on Washington psychologist Jeanette Paroly. Critics call the therapy "pseudoscience."Researchers have found EMDR to be better than nothing, but no more effective than exposure therapy alone. Proponents say it can treat post-traumatic stress disorder in three sessions.