A military engineer assigned in 1980 to test the drinking water at this sprawling Marine Corps base punctuated his findings with a handwritten exclamation point.

"WATER HIGHLY CONTAMINATED WITH . . . CHLORINATED HYDROCARBONS (SOLVENTS)!" William C. Neal wrote in capital letters on one of his surveillance reports in early 1981.

A private firm followed up with tests the next year. One of its samples showed an astonishing result: 1,400 parts per billion -- 280 times the level now considered safe for drinking water -- of trichloroethylene, a likely cancer-causing chemical used for degreasing machinery that can impair the development of fetuses, weaken the immune system, and damage kidneys and livers. Other samples showed as little as 1 part per billion to as many as 104 parts per billion -- more than 20 times the level now considered safe -- of tetrachloroethylene, a toxic dry-cleaning chemical that can seep into body fat and slowly release cancer-causing compounds.

The number of people who may have drunk the tainted water, bathed in it, had water fights with it is staggering: The Marine Corps estimates 50,000 Marines and their families lived in base housing areas that may have been fed by the wells before they were closed in 1985. Victim advocacy groups place the figure even higher, at 200,000, which would make Camp Lejeune one of the largest contaminated-water cases in U.S. history.

Already, more than 270 tort claims have been filed with the Navy's judge advocate general's office by former residents, who are required by law to file claims with the military before proceeding with any possible action in civilian courts.

One of those claims was filed by a Marine air traffic controller named Jeff Byron. Within months of the 1982 tests, Byron moved his family into base housing at Lejeune, grateful to leave behind a rickety mobile home in favor of a modest townhouse with a postage-stamp back yard. Byron and his wife, Mary, were not told about the water-sampling results, and nearly two decades would pass before they would find out about them. Now he wakes up thinking about all the frozen lemonade and apple juice he mixed with tap water for Andrea, who was born three months before he moved on base, and for Rachel, who was born two years after.

Both of his girls have been beset with a lifetime of ailments: Rachel, who is developmentally disabled, was born with a cleft palate and needed leg braces as a child. She has spina bifida; a gangly, arachnoid cyst on her spine that cannot be removed; and brittle, rotting teeth. Andrea had a rare bone marrow syndrome known as aplastic anemia and has been told by her doctors that the disease could recur if she becomes pregnant.

"I find myself asking, 'What if I hadn't joined the Marine Corps?' " said Byron, who left the military for the private sector in 1985.

No one knows for sure whether the water at Lejeune made Byron's children ill or whether it sickened thousands of other former residents -- both Marines and civilians living on base -- hundreds of whom have organized into a lobbying group known as Water Survivors. The group's members blame the contamination for a variety of ills, from chronic headaches to virulent cancers, from infertility to the incurable leukemia that claimed their children's lives.

The battle over the water contamination at Lejeune has strained age-old loyalties, matching Marine veterans against the power structure of an organization that prides itself in the motto Semper Fidelis, or "always faithful." The Marine Corps has not denied that contamination took place at Lejeune.

In a written response to questions from The Washington Post, the Corps said the wells were not shut down for five years because there were no federal drinking-water regulations then for the chemicals found in Lejeune's water: trichloroethylene, or TCE, the metal degreaser that federal researchers say was kept in leaky underground storage tanks, and tetrachloroethylene, or PCE, which researchers believe leaked into the wells from a dry cleaner that still operates across the street from Lejeune's main gate. The Environmental Protection Agency had recommended levels -- not enforceable standards -- at the time, and the Corps said the average contamination readings for TCE were below those levels and that the PCE readings were "only slightly above" those levels.

In recent months, the contamination case has drawn the attention of the EPA's criminal enforcement division, which has dispatched investigators to gather information about the history of contamination at the base. There also is pressure on Capitol Hill. Sen. James M. Jeffords (I-Vt.), the ranking minority member of the Senate Environment and Public Works Committee, says hearings are warranted.

"I have very serious questions about why the Marine Corps, who knew the drinking-water wells were highly contaminated in 1980, didn't close them until 1985," Jeffords, a Navy veteran, said in an interview. "Sunshine is always the best disinfectant. . . . We have a strong obligation to provide all the information we already have to the Marines and their families."

For many former residents, the contamination saga did not begin until 1999, when they received questionnaires from the Agency for Toxic Substances and Disease Registry, or ATSDR, which studies polluted Superfund sites, such as Lejeune.

The ATSDR, which focused its research on women who were pregnant while living on base from 1968 to 1985, issued a progress report in July that identified 103 cases of birth defects or childhood cancers among nearly 12,600 births included in the survey. Jeffords and his research staff say the rate is three to five times the normal rate.

The Marine Corps has vowed to cooperate with the study. In a videotaped statement accompanying the public release of the ATSDR progress report, Lt. Gen. Rick Kelly, deputy commandant for installations and logistics, said, "I want you to know that the welfare of our extended Marine Corps family is very important to the commandant and me." He closed his remarks with the words semper fidelis.

The release of the ATSDR report came after three years of often bitter clashes between members of Water Survivors, who used the Freedom of Information Act to gather mounds of evidence that they say proves federal officials have not been forthcoming about the contamination, and the Marine Corps and federal researchers. In a series of 1998 e-mails recently disclosed on the Marines' Web site, officials at Lejeune discussed how public concern about water contamination could be stoked by the release of the film "A Civil Action," which traced the legal battle over contaminated drinking-water wells in Woburn, Mass.

"Just a thought," Neal Paul, director of Lejeune's toxic cleanup program, wrote to an official at Marine headquarters. "With the movie coming out in Dec., can we delay the questionnaires until April/May time frame?" An ATSDR spokesman said the timing of the survey was not influenced by the Marines.

The ATSDR estimates that the Lejeune wells may have been contaminated as many as 30 years before being closed -- going back to the mid-1950s -- a projection that would greatly expand the number of potential contamination victims to encompass the massive buildup of troops at Lejeune between the Korean and Vietnam wars. Marine Corps officials described the projection as "opinion or conjecture" in its written response to questions.

Extending the contamination dates to the 1950s would draw in veterans, such as Tom Townsend, a retired Marine major, whose wife, Anne, is ineligible for the study because she was pregnant with their third child, Christopher, in 1966 -- two years before the start date of the ATSDR study, which was chosen because it marks the beginning of computerized birth records in North Carolina.

Christopher always had a "strange cry," Anne Townsend recalled, "not a healthy, full-wallop cry." Christopher's father, who was on duty in Vieques, Puerto Rico, got home just in time to see him die of a heart defect when he was 3 months old.

Tom Townsend trades documents and talks strategy with Jerry Ensminger, another retired Marine once based at Lejeune, whose eyes still well with tears when he talks about Janey, the 6-year-old daughter he lost to leukemia in 1985. Ensminger said he wonders whether doctors would have been able to change her treatment if they had known about the contamination.

For Townsend and Ensminger, one of the most galling pieces of paper they have unearthed is a notice sent in 1985 to residents of Tarawa Terrace, a large housing development at Lejeune where Byron and Ensminger once lived, by the base's then-commander, Maj. Gen. Louis H. Buehl. The notice announces the closure of two wells because "minute (trace) amounts of several organic chemicals have been detected," though it does not specify which chemicals were found.

Some water-contamination experts believe the lack of enforceable regulatory standards for the chemicals would be a weak defense if the case ever made it into the courts.

"Even in those days, that would have constituted pretty close to a drinking-water crisis," said Richard Maas, director of the environmental studies department at the University of North Carolina at Asheville. "That information was all out there; it was being used in the late 1970s and early 1980s. . . . If a typical town had done that [sampling], they probably would have abandoned that as a water source."

Finding out who may have been exposed to the tainted water at Lejeune is proving to be a monumental task. The ATSDR is poring over aging maps and pipe diagrams to glean where the water flowed and when. The research is further complicated by the transitory nature of military life -- many of the Marines who may have consumed tainted water lived on base for only a few years and have since moved.

The ATSDR has been assailed by the Water Survivors group and by Jeffords for limiting the scope of the study to pregnant women.

"We didn't want the whole world to know, or they'd all start calling -- we couldn't handle that," said Marie L. Socha, an ATSDR researcher who has worked on the Camp Lejeune project.

The agency has determined that the chemicals would not affect the health of adults, a contention disputed by Michael Gros, an obstetrician at Lejeune from 1980 to 1983. Gros, who has T-cell lymphoma and can no longer practice, has been pushing for the ATSDR to notify all former residents, regardless of age.

"They've just done the biggest ghoulish experiment on adults, and they don't want to know the results," Gros said. "What's happening while they're stalling us is everybody's gone hither and yon, and they're dying."

Leaders of the Water Survivors group, increasingly skeptical about the pace of federal research, are hoping the possibility of congressional hearings could speed their efforts to get compensation for the medical bills of possible victims.

"We want to force these people, under oath, to come in and talk about this stuff," Gros said. "How do you know your water is contaminated for five years and do nothing about it? How do you explain that away?"

But, for all the passion, some of Ensminger's old Marine pals want him to let up.

"They say, 'Semper fidelis -- give 'em a break. Why do you want to hurt the Corps?' " said Ensminger, a former master sergeant who retired in 1994 after 241/2 years in the Corps.

But an image that rattles around inside Ensminger's stubborn, crew-cut head will not let him give up. He sees Janey, all big, brown eyes and silly smiles, watching him as her doctors advised him to stop treatment because there was no hope. Janey looked up at them, Ensminger recalls, and said: "You're talking about me. I'm not dead. You're not giving up on me."

One week later, she was gone.

Jerry Ensminger retired from the Marines in 1994 and has been fighting for details about water contamination at Camp Lejeune, N.C. Thousands of Marines and their families lived in areas that may have been fed by tainted wells.Ensminger spent 241/2 years in the military and believes that his children were affected by contaminated water as they were growing up at Camp Lejeune.