What had been a dormant trend of robbers targeting college drug-dealing operations around Philadelphia resurfaced Sunday night, when - a block from Temple University - armed men robbed a student rowhouse from which marijuana was being sold, police said.

The four Temple students home at the time had left the front door unlocked, allowing the three men believed to have been watching the house to walk right in, police said. With handguns trained on them, one of the students took a robber upstairs, where the student handed over an unspecified amount of cash and drugs. The armed men then fled the house on the 1500 block of Page Street, though not before taking the students' cellphones.

Such incidents were a regular event around Philadelphia's campuses last year, with enterprising criminals targeting student dealers who lacked the security typical of larger drug operations. But without explanation, the phenomenon had fallen off in the neighborhoods around Temple, in North Philadelphia, and around Drexel University and the University of Pennsylvania, in West Philadelphia, since the school year began, police said.

Capt. Branville Bard, whose 22d Police District covers Temple, suggested that students might be dealing less because of the earlier robberies.

"It's just speculation," he said. "This is the first case I've seen since September."

Before that, police reported seven drug-related home invasions around Temple over 11 months. And four such crimes were reported around Drexel over 17 months.

Temple students have long maintained an uneasy relationship with the high-crime neighborhoods surrounding them. And with more students choosing to live close to the university over the last decade - enamored of the prospect of living in Philadelphia and being close to its artistic and nightlife offerings - young men and women clad in red university sweatshirts and caps are becoming familiar sights for the largely low-income families living in the area around campus.

On Monday, with classes wrapping up for the year, students near the site of the robbery said that despite the surrounding crime, the neighborhood was relatively safe.

"This is a big city. And the majority of the students who come here are from suburban areas, and they think nothing of walking home at 11 o'clock at night after working on a paper or something," said Joe Herman, 22, a Temple senior. "Those kids were just being stupid. They brought people into their house they didn't know and they were selling drugs and got robbed. They know the area they live in. I can't feel bad for them."

One of the students robbed Sunday, Massimo Pulcini, 21, was charged Monday with drug possession with intent to distribute after police found marijuana in the house. Charges were also being finalized Monday evening against a man stopped shortly after the robbery within a couple of blocks of the Page Street home. Police say they believe he was involved in the crime.

The two other robbers remained at large Monday. One was described by Temple police as a black man age 18 to 25 with a chubby build, wearing a black hooded shirt. The other was described as a black man wearing a light-brown shirt with white lettering.

As news of the incident spread around campus Monday morning, university officials e-mailed students, urging them to keep doors and windows locked and to report to police any suspicious or criminal activity involving roommates or neighbors. University spokesman Ray Betzner said Temple police were working with city police to increase patrols in the area.

Betzner declined to comment on whether Pulcini would face disciplinary action from the university.

Police did not release the names of the two men and one woman who were in the house with Pulcini at the time of the robbery.

The situation facing Temple - trying to keep students safe in a low-income city setting - is one that Penn has spent the last 15 years trying to minimize through expansive real estate development projects in West Philadelphia, said Lt. John Walker of Southwest Detectives.

"When you push out into urban areas around Temple, you're pushing into neighborhoods that have been violent for years," he said. "Penn was very aggressive."

As Temple students started preparing for the beginning of finals on Thursday, some of their neighbors were still in shock.

Kiana Williams, 28, who lives near the crime scene, said she was stunned by the news of the robbery and arrests, adding that there were no signs of drug sales in the block.

"It's pretty nice around here. I would not expect something like that," Williams said of the robbery. "All I heard was that it was a home invasion. I kept saying to myself, 'Why would they go into a house like that?' I'm shocked. I'm still shocked."