Two undergraduates were robbed at knifepoint by two assailants at 12:40 a.m. on Tuesday morning in front of 100 Walker St., which borders the Quad, according to a statement released by the Harvard University Police Department (HUPD) yesterday.

The two suspects, who are described by the HUPD as black males 18 to 20 years of age, have not been apprehended.

One of the victims, a Currier House resident, said the two assailants ran from Linnaean St. towards him and his friend, a Pforzheimer House resident.

"I thought it was friends of mine, and I thought it was a joke until I saw the knife," he said, speaking on the condition of anonymity.

"They were shaking, really scared," he said. "Basically, the guy put a knife to my belly. I couldn't see it, but definitely could feel it."

The assailants demanded money from the students and fled after the Currier House resident surrendered his wallet, according to the student.

HUPD Chief Francis D. "Bud" Riley said police are looking into a possible connection between this robbery and one that occurred Tuesday night near the Peabody School, at 44 Linnaean St.

"To the best of our knowledge these are unarmed robberies," Riley said, contradicting the Currier student's account.

"We have had detectives working with Cambridge [police]...to work on any connections," the chief said.

Police distributed an advisory around the campus to make students aware of the incident, said HUPD Spokesperson Peggy A. McNamara.

Riley said police are also taking extra security measures near the Quad.

"We have increased patrols in the area, distributed descriptions of the subjects to officers [and] we have plainclothes and uniformed detectives in that area," Riley said.

Nonetheless, Riley urged students to be careful.

"I give the same caution to students as always: be aware of what's going on around [you]. If you feel a sense of unease, you should use safety phones to contact university police," he said.

Quad students said they were surprised and concerned about the incident.

"I feel less safe," said Dan M. Ring '99 of Pforzheimer House. "I took it for granted that since we're close to a residential neighborhood we could take safety for granted."

Scott J. Waldman '99 of Cabot House said the news will not have an effect on his habits.

"It does kind of wake me up though. I thought that was restricted to Mather," he said.

Other students expressed fear that their daily routes were unsafe.

"It's disappointing that there's no sense of security," said Willard R. Huval '71-'97, of Pforzheimer House.

Huval lives in Jordan, which is located on Walker St. near where the incident occurred.

Huval said he was concerned that his "daily route between the dorm and the bus" may be insecure.

But the Harvard Shuttle Service said students could request to be picked up by Escort Service on Walker St. instead of walking to the regular stop in front of Currier House.

"If we know that it's one or two students, we will pick them up on Walker St., but if it's three or more, we'll ask them to wait at the shuttle stop," said a Shuttle Service operator. "There's safety in numbers."

Quad house administrators had varied responses to questions about the incident. Pforzheimer House tutors had not been formally informed of the incident. Some Pforzheimer tutors said they were surprised and dismayed that they were not immediately informed. The masters and the Alston Burr senior tutor were unavailable for comment.

Currier House Master William A. Graham said the administration was "working as a quad to inform students and warn people." Currier Senior House Tutor John Stubbs said his house plans to inform students through a public notice such as individual notices in mailboxes.

"This was certainly a surprise. [It] will be discussed in tutor meetings and in study breaks," said Graham. Though students will be warned, he added, "there is only so much you can do."

"It's important not to be alone, to be wary and alert. About 99 percent of these things can be prevented," he said.

But Graham stressed that the students had been following recommended safety procedures.

The HUPD released the following description of the two suspects yesterday: One is a 5'7" black male of medium build, 18-20 years of age, who was unshaven and wearing a green jacket with a hood. The second suspect is a 5'10" black male of medium build, 18-20 years of age, who was wearing a white cloth sweater with a hood