Dyke Marsh, a federal wildlife sanctuary along George Washington Parkway south of Alexandria, is a secluded spot on the Potomac River for birds and bird watchers.

It also is a popular hangout for homosexuals.

Lately, the bird watchers claim, the influx of "gays" -- who routinely and unabashedly encounter one another in the rustling bushes away from the marked trails -- has become a form of nature loving that threatens the sanctuary's environment.

"They're like cockroaches," one area conservationist says. "I chase them out on occasion, but they keep coming back. They've built up a vast network of unauthorized trails, compacting the earth, trampling the vegetion. They've just penetrated the woods."

U.S. Park Police say they have received complaints from citizens concerned not only about Dyke Marsh but also about other homosexual rendezvous points along the parkway, including Turkey Run, Columbia Island and the Iwo Jima Memorial, where a homosexual was beaten to death two years ago.

"After we tried to clean up Iwo Jima," said Tom Lam, a park police-man who has made more than 20 arrests for sex offenses committed in the area near Belle Haven park, "they all moved down to Dyke Marsh. If they (the park police) don't get public pressure, they won't do anything about it."

After the Iwo Jima murder, undercover park police made numerous arrests near the memorial and at Dyke Marsh, but relaxed their patrols after complaints of harassment from homosexual groups.

Adjacent to the Belle Haven picnic area, Dyke Marsh is a 26-acre haven of woods and wetlands offering a rich combination, bird lovers say, of land, swamp, and river birds, warblers, long-billed marsh wrens, and mergansers.

Ironically, the angry bird watchers may succeed at the marsh where the police have failed. Their complaints are based on environmental concerns as opposed to moral or legal ones.

The National Park service acknowledged last week that Dyke Marsh is of particular concern because of its fragile ecology and said they have already begun efforts to replace some of the marsh's vegetation destroyed by the homosexuals.

"It has been alleged that the increased homosexual activity is harmful to the area," said parkway super-intendent Don H. Castleberry. "We are exploring the possibility of closing off the trails, putting up signs, etc. It's a resource, rather than law enforcement problem at this point. We don't know the extent of it (the damage) yet."

"At the same time," park service spokesman George Berklacy said, "it's a public park. Whether visitors are heterosexual or homosexual should not be of concern to the National Park Service."

According to arrest records obtained from park police, the men who frequent Dyke Marsh and other wooded areas looking for sexual partners are mostly white males in their early 30s from the Northern Virginia suburbs. The youngest was 16, the oldest 62.

Close to 100 men have been arrested at the Marsh and Iwo Jima monument in the last six years, charged with committing indecent acts, soliciting, sodomy, indecent exposure, resisting arrest and "disorderly sex."

"We've arrested a government architect, a lieutenant commander in the Navy, a lieutenant colonel in the Army, diplomats, congressional aides, clergymen and one policeman," said a park police officer who worked undercover two years ago, patrolling the parkway haunts.

"Some get hysterical. One man fell down and started screaming and kicking. He said we should shoot him right there because his career was ruined," said the officer who asked to remain anonymous.

"It's kind of a dirty job," he said, adding that "every one we arrested in pairs were strangers to each other."

Members of the homosexual community say only a small percentage of homosexuals frequents the parkway haunts.

"It's rather crude and impersonal," said one homosexual who has visited Dyke Marsh, "but we don't bother anybody.We try to stay off the trails."

"The problem is a persistent one," said Bob Davis, president of the Gay Activist Alliance in Washington. "The people who participate in 'bush sex,' as we call it, are too scared to go to bars. They're probably married so their sexual life is underground. They know the dangers are there, but they're desperate."

Dan Hoehne, a park police officer who is also secretary of the environmental group, Friends of Dyke Marsh, says, "It's a cat and mouse game. They've got one eye on their partner and one eye on police."

According to Hoehne, the police now "look the other way. I would say our hands are tied."

Dyke Marsh, according to Alexandria City Council member Ellen Pickering, has turned into "one long battle" between the bird watchers and the homosexuals.

"They (the homosexuals) may feel safer there than at Iwo Jima," she said. "The numbers seemed to increase after the violence there, Birds of a feather flock together, I guess."

On Oct. 2, 1976, the battered nude body of Ronald J. Pettine, 32, was found in the wooded area near the Iwo Jima memorial. The 17-year-old youth convicted of the murder testified in his defense that he went there only "to smack around a few queers."

Since then, Dyke Marsh, whose name is drawn from the manmade dike that helped create it years ago, has become more popular and police say there is a possibility of violence there.

"We've heard about a few muggins," said one officer. "But most of them would never report any crimes for fear of being identified as homosexual."

Police say the number of homosexuals at Dyke Marsh is highest on summer days when more than 100 may converage on the area, the younger ones wearing "hot pants," the older men with binoculars around their necks. The sexual activity takes place day and night.

One workman at the Belle Haven Marina adjacent to the marsh warned a visitor one afternoon last week not to walk into the marsh alone. "There are a lot of suspicious characters hanging around," he said.

"Iwo Jima has been in the papers," said one park police officer. "The park service doesn't seem to care about Dyke Marsh. People don't know about these other places until something happens and it makes the news. The park service doesn't like to admit there's a crime problem there."

The officer said Dyke Marsh "is hardly ever" patrolled, although at Iwo Jima there are policemen driving by "two or three times a night." At Turkey Run, he said, police are there "once a day."

"Eventually," said gay activist Bob Davis, "somebody will get hurt."