After weeks of apparent success in combating a spike in street crime that began last fall, four robberies this week offered the first serious test of whether the University’s response has been sufficient to maintain security on and around campus.

As the first major crimes around campus in six weeks, the robberies — at least two of which were armed, and all four of which were committed against members of the Yale community — could mark either a continuation of the fall’s increase in crime or simply a small setback for efforts to patrol the University.

Those questions are particularly stark because two of the robberies occurred before 7 p.m., and another took place at the intersection of Temple and Wall streets, where patrols have been heightened for months.

Yale Police have no reason to believe the four robberies are connected to one another or to the incidents that took place early last semester, Chief James Perrotti said. In addition to the robbery at Temple and Wall Monday night — in which the perpetrator pointed an unidentified object at the victim — the reported crimes included gun-point muggings at Dwight and Elm streets and at the Bank of America near Lynwood Place and Elm Street, as well as a purse-snatching on Orange Street.

According to New Haven Police Department records, about 12 assaults and 12 robberies were reported in and around the area where the vast majority of Yale College students live between late August and mid-November.

“We continue to think that the plan of additional police deployment has been effective,” said Yale Deputy Secretary Martha Highsmith, who oversees campus security. “Compared to the prior six weeks, certainly they are an aberration.”

During the course of the academic year, the University’s response has developed along two lines — a stronger police and security presence in problematic areas and a publicity campaign to discourage students from walking alone at night.

The new security measures instituted in the fall included an increase in patrols of uniformed police officers at night, the installation of new blue phones and the hiring of about a half-dozen new security guards, Yale officials said.

The focus of the additional patrols highlights the areas that have raised new concern — the Wall and Temple intersection near Silliman and Timothy Dwight colleges, the area behind Payne Whitney Gymnasium, the area around Park and Howe streets that includes off-campus housing, and a neighborhood up Prospect Street that is frequented by graduate students.

After the incidents this week, Yale police also decided to assign an additional unmarked car to patrol central campus, Highsmith said. In the coming months, the department also plans to hire 10 new officers, raising the size of the University’s police force to 83.

The increased patrols have not resulted in a corresponding increase in arrests — the vast majority of last fall’s crimes, and all four this week, remain unsolved. Yale officials, however, said they believe the police presence has worked as a deterrent.

“Just the process of letting people know we were around … seemed to have an effect,” Perrotti said.

Highsmith also attributed the relative calm at the end of last semester to a change in student behavior. While the security escort service had averaged 500 calls a month during the 2004-05 academic year, calls for the service topped 2,000 in October, November and December.

But the two early evening crimes this week were committed at an hour when many students are less likely to call Yale security. Pierson College Dean Amerigo Fabbri said the Pierson student who was mugged in the Bank of America parking lot told him he did not think he needed to take precautions so early at night.

“I know that everybody is kind of concerned,” Fabbri said. “They are as cautious as they can be, but sometimes it is not enough.”

In addressing the dynamics of crime in New Haven, University officials said the numbers could be the function of a wide range of other factors, from the weather to the availability of after-school programs.

In prior years, Yale has often seen crime go up in the winter, as daylight hours grow shorter and criminals concealing weapons beneath heavy coats draw less attention. But with Yale Police attributing some of last fall’s crimes to local youths on bicycles, the colder weather may have pushed potential perpetrators off the streets. Although Yale Police believe the most alarming crimes last fall were committed by adults, officers have begun more vigorously stopping young bike riders for minor violations to deter threatening behavior, Highsmith and Perrotti said.

Likewise, community leaders also blamed cuts to youth programs — particularly in the summer — for leaving local teenagers with little supervision or support outside of school. Those criticisms led the city to announce its plans for a new $1 million youth initiative late last year.