In 1974, several dozen African American college students, all members of fraternities and sororities, gathered on a hot July weekend. They brought picnic baskets, played football, schmoozed and partied at a small park in the Germantown section of the city.

The idea stuck, and over the years word spread throughout the black fraternity and sorority network about the summer picnic in Philadelphia. Within a few years, the event had grown so large that the group moved to Fairmount Park, the city's flagship park.

Now celebrating its 25th year, the Philadelphia gathering of African American fraternity and sorority members, which includes weeklong events culminating with Saturday's Greek Picnic, is the oldest and largest of such fetes. Last year, more than 175,000 people--many of them affiliated with black Greek-letter organizations and coming from New York and Washington and cities in between--came here for the picnic.

"It should be one of the better parties of the year," said Shawn Smith, 21, a chemical engineering student at Drexel University in West Philadelphia, looking forward to the weekend's events. Although not a fraternity member, he will be attending his third picnic. "I have to party to relieve the stress," said Smith, who also takes classes during the summer.

The Greek picnic has grown to what its original participants could never have fathomed--a local tradition, one of the city's largest annual events and one of the nation's largest gatherings of black young adults. (The average age of last year's attendee was 19.) But the success of the picnic has been tempered in recent years, as rowdy after-picnic crowds spilled aimlessly into the streets of Philadelphia, fostering complaints from residents about noise, traffic congestion and disorderly conduct.

But last year may have been the nadir. Numerous sexual assaults and at least one clash with police officers marred the picnic weekend and were captured on amateur videotapes that aired dramatically on local television news in the days after the picnic.

Most disturbing were the reported incidents of "whirling," where groups of men surrounded a woman, touched and fondled her, sometimes pulling pieces of clothing off, and then ran away. At least four women reported such sexual assaults in the park after the picnic was over and similar incidents were reported at hot spots such as South Street, where party-goers congregated after the picnic, according to police.

Gatherings of black college students in cities such as Virginia Beach and Atlanta, as well as traditional spring break haunts in Florida beach cities, have had similar problems in recent years. In many cases, organizers have laid blame for trouble on "outsiders."

In Philadelphia, Greek picnic organizers, while acknowledging that such publicized incidents have reflected negatively on the gathering, are adamant that the troublemakers are not fraternity and sorority members, but local youths crashing the party. And while outsiders are welcome, they say, lewd, uncivil and illegal behavior is not.

No arrests were made in last year's incidents, because the women couldn't identify their attackers, police said.

But no matter who's to blame, picnic co-chair David Warren said, "We're concerned about the perception of the event, and we want to make sure people are safe."

To that end, picnic organizers have worked closely with city officials and police to ensure that this year's anniversary event comes off without a hitch. For starters, more uniformed and plainclothes police officers will be patrolling both the picnic grounds and city streets where late-night partiers congregate. Members of local civic groups, including the Masons, have volunteered to act as monitors, keeping their eyes and ears open for any incidents.

And for the first time, the city has set up a special night court with three judges to hear cases immediately. The court sessions will start at 9 p.m. Saturday. But city officials aren't discouraging the affair, which pumps about $24 million into the local economy.

"We are not turning this into an armed camp," said Police Chief Inspector Dexter Green, who is in charge of policing the picnic area. "But we want people to feel comfortable coming out and having a good time."

This year, picnic organizers also are trying to broaden the event and change its reputation as a mostly college-age party. They have planned several events for older Greeks, such as a golf tournament, and are hosting a new family activities area, with clowns, face painting, musical performances, a raffle of education savings bonds and a moon bounce.

Officials also are trying to focus attention on the nonsocial aspects of the picnic--college recruiting and scholarship information, an on-line job bank, and the chance to network with what many hope will be the next generation of black leaders.

With the new events and added police presence, organizers are hopeful that they can shake the negative images of past picnics.

"Once this thing goes off flawlessly this year, we can change the image certain people have that this is a negative event," said Gregory Wright, president of the Philadelphia Alumni Chapter of the National Pan-Hellenic Council, an umbrella organization of nine national black fraternities and sororities. Nationally, some 1.5 million African Americans, both students and alumni, belong to these organizations.

"We're taking the picnic back," said Rita Tolbert, who attended some of the early picnics and then stopped going while she pursued a career and raised a family. Tolbert, now an event co-chair, said that when she visited some local Greek chapters in recent months, some women expressed safety concerns about coming to the picnic.

Some of the younger participants, however, seem nonplussed about the controversies. Burgundi Allison, 20, a junior at Morgan State University in Baltimore, said she witnessed a whirling incident after last year's picnic but isn't worried it could happen to her. "I'm not condoning what happened, but it has to do with how a lot of females present themselves," she said. "Being a lady, I don't expect that to happen to me."

And most certainly, it's not enough to keep her away from the picnic. "This Saturday the place to be will be Fairmount Park," Allison said. "Everybody will be there, from all the schools and home towns."