For the past four decades, few San Franciscans have had a better window onto the changes in Dolores Park than Douglas Du Frene.

Since 1977, Du Frene has lived in his handsome three-story home at 20th and Church streets on the park’s southwest side. The house boasts an extraordinary view of the popular park’s sloping green hills and the downtown skyline beyond.

Over the years, he has watched the park slowly transform from a gritty and squalid mound, where he routinely rebuffed pushy pot dealers, to a jewel of the city’s park system. Fresh off a two-year, $20.5 million renovation, Dolores Park can draw a crowd of 10,000 revelers on a warm and sunny weekend day.

“Years ago, my partner and I would lay down in the sunshine and there would be 75 people there,” Du Frene said. “It’s not like that now.”

Frustrations about conditions in and around Dolores Park have taken a darker and more urgent turn in recent months following a rash of violent confrontations in the park, capped by a potentially gang-related triple shooting Thursday that left two men in critical condition.

For the past few years, many residents like Du Frene who live near the park have had to deal with the raucous noise, excessive drinking and mountains of litter that often accompany the weekend bacchanals.

“It’s no longer a place I want to go. It used to be peaceful; now it’s just a place to drink and party on the weekends,” said Steve Hall, who has lived near the park on 19th Street since 1985.

Sarah Madland, a spokeswoman for the Recreation and Park Department, said in an email: “We have significantly improved the trash, public urination and amplified sound issue that used to plague the park. While there is always more to be done, we are so happy with the progress we’ve seen in these areas since the park reopened.”

The weekend parties and recent violence, combined with a persistent homelessness issue and what longtime residents describe as progressively brazen drug dealing, have some in the neighborhood surrounding the park calling on the city to ramp up its police presence to clamp down on criminal activity.

“We pay taxes. The city should come and make sure things are clean, and (the police) should have a full-time presence here,” said Mary Charles, whose home on Dolores Street, where she has lived for 38 years, faces the park’s east side. “I still love the neighborhood, but it would be good to have more police around here.”

Last month, police clashed with about 400 people at the park after breaking up an impromptu downhill skateboarding competition along Dolores Street on the southern edge of the park. Tensions smoldered for more than an hour, with some people throwing objects at police.

Two days before that incident, a 20-year-old man was stabbed in broad daylight following a brawl that witnesses said involved about 15 people. The man suffered non-life-threatening injuries.

In mid-May, a 23-year-old man was hospitalized with life-threatening injuries after he was swarmed by five assailants who beat him with bottles and a golf club. Police said at the time that the attack was not random and were investigating whether the attack was gang-related.

And last year, a 25-year-old man was attacked and stabbed in the torso by a mob of 10 men. The victim didn’t know the men and told police he assumed some were gang members.

“It’s a beautiful park and it’s a fantastic neighborhood, but at the same time, there shouldn’t be criminal activity there and people hanging out who obviously aren’t up to any good,” said Peter Lewis, president of the Mission Dolores Neighborhood Association. “There needs to be regular patrols with people in uniform, and the people who have this prejudice against cops need to get over it because we need law and order in a big city.

“Enforce the laws and back up the police — that’s the message to the mayor and all the supervisors and the district attorney,” Lewis said.

“It sounds terrible for me to say that as a liberal, but I think more police is the answer here,” said Paula Ingram, who has resided on 18th Street since 1995. Ingram added that she was “increasingly concerned about the drug dealing that goes on at the bottom of the footbridge” that links the park to the intersection of 19th and Church Streets.

Ingram and numerous other residents say the footbridge and the archway beneath it are hot spots for drug dealing, prostitution and vagrancy. On a recent Monday morning, a young man standing atop the bridge with a swollen backpack could be seen openly hawking marijuana to passersby. The altercation that resulted in Thursday’s triple shooting began on the bridge.

“It really worries me. There’s more violence and homelessness on the street than there used to be,” said Kaye Hoxter, who can see the park from her home on 18th Street. Hoxter said she feels particularly vulnerable because she uses a wheelchair.

“If violence comes out of the park, it’s going to come to me. That’s my green space, that’s my park,” she said. “But I don’t go there anymore.”

In response to the triple shooting, the San Francisco Police Department has added to its daily foot, bicycle and car patrols of the park and the surrounding neighborhood, said Capt. Bill Griffin, who leads the department’s Mission Station.

Griffin said that although his officers have come in contact with people believed to have gang affiliations at the park, “I wouldn’t equate that to a large gang presence there.” He added that the Police Department is also working more closely with rangers from the Recreation and Park Department.

Overall, the number of reported incidents at the park is in keeping with historical averages, which tend to rise in the summer. The investigation into the triple shooting last week is ongoing, Griffin said, as police continue to work to identify the attackers.

“I think the park is a safer place. Our officers are out there,” Griffin said.

The recent violence has prompted Supervisor Jeff Sheehy, whose District Eight includes Dolores Park, to call a community meeting for Aug. 21 that will help city officials gather information on how to make the park safer. The triple shooting last week, Sheehy said, “demands a top-to-bottom review of Dolores Park operations and a community process on how to make things better.”

As Du Frene looks back on the decades he has spent alongside the park, he said his affection for those 15 acres of green space has never abated, and he’s confident that Dolores Park’s problems will be solved.

Despite the crowds and the littering and the occasional smartphone snatching he has witnessed, Du Frene said he’s heartened by the “Love Dolores” campaign flyers he sees circulating throughout the neighborhood — the effort to encourage visitors to take care of the park and clean up after themselves is supported by numerous neighborhood businesses and organizations.

“I love the park. I always have,” he said.

Dominic Fracassa is a San Francisco Chronicle staff writer. Email: DFracassa@sfchronicle.com Twitter: @dominicfracassa