Shortly after midnight Aug. 16, as late-night diners left the trendy Capitol Hill restaurants along Pennsylvania Avenue SE, five Marines broke from a throng of nearly 150 rowdy people shouting anti-gay slogans and burst into Equus, a homosexual bar and restaurant.

A brawl broke out amid the name-calling and the yelling. One bar owner was punched in the eye, windows were smashed, egos were bruised.

By the time D.C. police arrived in force to quell the disturbance, an incident among strangers had grown into a showdown of will and threatened masculinity. One one side, U.S. Marines -- Leathernecks, America's toughest fighting men; on the other side, proud, out-of-the-closet gay men determined not to be humiliated or defeated.

A rally at the bar last night drew a large crowd. Representatives of the mayor's office and the U.S. Civil Rights Commission made appearances at the bar and a couple of Marine officers in civilian clothes drove around the area watching for possible trouble. There were no incidents.

For some, the battle lines had been formally drawn.

"Gays have been bothering some (Marine) joggers in the morning," said a young Marine, angry and combative, sipping beer several days later at a bar near the Marine Barracks at 8th and I streets Se. The Marine, from a small town in New York, asked not to be named.

"Gays are out trying to pick up dates," he said. "The guys in the barracks are pretty upset about all this gay stuff. All I can say is that after this, the gays better watch out."

Several blocks away, Equus coowner Rick Holloway, who got a blackened eye in the incident, said, "We never bothered them. They were welcome to come here and drink. They came in here calling us faggots, trying to get some of the customers to fight them.

"This is the sixth incident with Marines we've had since we opened four months ago," Holloway said. "They think that we are not men. They think that all homosexuals are frills and feathers. I am a man. And, I will stand up and fight."

Col. John P. Monahan, Marine commandant, said, "The publicity that has come out of this has blown the whole situation out of hand. We are investigating five men and two men have been arrested and charged.

"I've instructed the troops unofficially to stay away from those bars," Col. Monahan said."There is a problem because of the area, but I really don't know why this has happened. I don't think they were up there to bother gays, but went up to have a good time.

"We're talking about the actions of a few men," he said. "My Marines serve the community in a lot of ways. I have some of the best troops in the world. They are clean-cut kids."

For 20 years Capital Hill has been a study in the juxtaposition of disparate lifestyles -- not without some tension -- between the poor gradually being displaced by the affluent, between the military and nonmilitary residents and between homosexuals and heterosexuals.

But the tacit tolerance of differences among residents and merchants was jarred by the Equus incident one week ago. In its aftermath, residents, city and Marine officials and merchants alike are bewildered.

"There has been a lot of talk in the community," said Advisory Neighborhood Commissioner Julie Servaites. "People are saying this is horrible, and they can't believe it's happening . . . This threatens the peace of the neighborhood."

The Equus incident brought to the flash point long-simmering tensions. It heightened resentment between some gays and some Marines who have credited each other with invasions of "turf" for several years.

Marines recent homosexuals who used the two Jima Memorial in Arlington, almost sacred to Marines, as a meeting place and spot for sexual activity. Two Marines were arrested and charged with assault on a homosexual there in May, but have not yet been tried.

Gays resent some Marines invading gay and lesbian bars and yelling derogatory epithets. Last October, for example, a Marine allegedly threw a tear-gas bomb into Phase 1, a lesbian bar on Capitol Hill about two blocks from the barracks, according to the bar's owner, Pat Sullivan.

Equus, 639 Pennsylvania Ave SE, was once considered a Marine bar. Then it was called Barb's Place, a topless bar. Some Marines resent the recent change.

"It's as if something they regarded as theirs was taken over by something they regard as a threat," said one senior Marine officer in the Washington area, a homosexual, who asked not to be identified.

One former Marine, who now openly acknowledges that he is gay, said that he used to take out his personal frustrations on homosexuals.

"When I was in the Marines, and still in the closet, I once went out of my way to make life difficult for a guy who many knew was gay," said Nick Maklary, an ex-Marine sergeant who was discharged honorably from the Marine facility in Quantico, Va. last February.

"I did that because I was very uptight about my own sexuality," said Maklary who, along with Billy Jones, an ex-Marine and director of the National Coalition of Black Gays, has formed GEMS -- Gay Ex-Marines, to help ease tensions.

"I used to humiliate him in front of other troops, and I felt a great deal of pain and frustration over my own gayness and somehow I thought I would feel better about myself if I took it out on him," he said. "I think we saw some of that frustration among some Marines at the Equus."

Maj. Paul Chapman, a spokesman for the Marines at the Pentagon, said the corps offers something to a man "looking for a challenge to prove whatever he wants to himself."

"We recognize that these kinds of problems (homosexuality and macho assertions of masculinity) come up, and we do offer psychological counseling, all the services do," Chapman said.

Marine officials would not speculate on how many Marines are homosexual. Chapman said, however, that he does not accept the usual estimate by gay activists that one of every 10 persons in the country is a homosexual. That estimate is based on the Kinsey report, which Chapman says he considers outdated.

"We do not run any surveys, and I'm not going to respond to spurious charges that 10 percent of the corps is gay," he said.

Chapman said that during the 1979 fiscal year, however, 83 Marines were discharged on grounds that they were homosexuals. The corps does not allow homosexuals in its ranks, he said. During the first 10 months of this fiscal year, 49 were discharged.

"The Mariners have deliberately cultivated the cult of manhood," said a gay Marine officer. "there is a lot of gay activity in the Marines. There have been male prostitution scandals at Camp Pendleton and other places. I don't think a very high percentage of Marines would be prepared to admit to themselves they are gay -- they use alcohol or drugs as an excuse to engage in sporadic gay activity."

Despite the tensions between some gays and Marines, gays say that many of them emulate the sterotypical image of clean-cut, muscular, tough Marines, especially at gay bars that cater to the leather, Levis and motorcycle crowd, like The Eagle downtown.

"The gay community is diversified, but certainly that kind of tough image is sought after by the guys who come into our bar," said Don Bruce, owner of The Eagle.

Gays, in a show of force, took their concern to the gates of the Marine Barracks Friday, holding a press conference that included most of the area's gay organizations, four D.C. council members, two candidates for council seats, and a representative of Mayor Marion Barry. Later that night Barry visited the bar.

Gay leaders also called gay rights supporters on Capitol Hill, including Rep. Paul (Pete) McCloskey Jr., (R-Calif.) and White House aides who promised to investigate.

"I called the Marine Corps liaison, and frankly, from what I am able to tell, it looks about even on both sides," McCloskey said. "All sides should just cool it."

"There is a real danger that if we don't react in a strong way right now, that we could be institutionalizing a running battle between Marines and gays for the next couple of years," said Melvin Boozer, president of the Gay Activist Alliance.

If gays are concerned about activities they believe threaten their rights, so too are some Marines.

"Why doesn't anyone write about the things that the gays do?" yelled a young Marine in a Barracks Row bar. "When we do something, the press comes around. But if it's the gays doing something, it don't get in the news. Sure some guys don't like gays. Gays bother them."

The young Marine, who asked not to be identified, sat in one of the few late-night drinking establishments near the Marine Barrcks on Capitol Hill that is not exclusively gay.

"A lot of Marines are not from areas like this," said another Marine walking down 8th Street toward a bus stop on Pennsylvania Avenue SE. "Things between Marines and gays have been building up for the past 18 months," he said. "That's all I can say. We're not supposed to comment."

The affluence that transformed Capitol Hill neighborhoods a decade or so ago into areas of $150,000 homes, has also changed the character of Barracks Row, a strip along 8th Street SE between I Street and Pennsylvania Avenue.

The shoe repair shops, dry cleaners, a movie house, and a couple of fast food restaurants still cater to the young Marines. But they have little to choose from late at night. Some places in the area do not welcome them.

Stuart Long, owner of four bars and restaurants not far from Barrcks Row -- Jenkin's Hill, the Hawk and Dove, Duddington's and Yolanda's A1 Campidoglio -- says he has talked to the Marine commandant about troubles he has had with Marines.

"Don't get me wrong, it's just a few who are the trouble-makers," Long said. "some of them are good customers. But others get drunk, try to pick up women at one of the bars and get frustrated, and the next thing you know, a fight has started. I don't need their business."

At the Barracks Row bar, the young Marine with his traditional 'white-walled" haircut, fingered his beer mug, his jaws tensing as he listened to a conversation among bar patrons discussing the Equus incident.

The young Marine blurted out, "People always want to s--- on us, we look funny, we look different because we have short haircuts. But when war comes, who do they call? They call us.

"We walk into a place, people look at us like we're inhuman," he said, his face reddening with anger. "Georgetown prices are high, and we don't have many places to go around here."