The Greenhouse Café in the Science Center will permanently stay open until 11:30 p.m. if evening patronage continues to rise, manager Marian P. Burns said yesterday.

The Undergraduate Council last spring asked the café to try out staying open for three extra hours on Monday through Thursday nights, but owner Robert Trager said that so far business has not been heavy enough for the plan to be economically feasible.

"We pay [the University] a lot of money" to rent the Science Center lobby space, Trager said, "and our operating costs are such that it costs us money to stay open." To stay open, the cafe, which sells cookies, sandwiches and yogurt, will have to attract at least 320 customers--200 more than now--during the evening hours, Burns said.

The Greenhouse set its new hours (7 a.m.-11:30 p.m., Monday through Thursday; 7 a.m.-2:30 p.m. on Friday) Beginning the week of September 17. Burns said the final decision on late hours will be made during the next two weeks.

The original suggestion for added hours came from a report by a subcommittee of the Undergraduate Council's Student Services Committee last April. The report cited the Science Center as "a popular late-night location," particularly for students using Cabot Library or the computer terminal rooms, and recommended that the cafe extend its hours at least for a trial period. "Oh, those cookies!" the report also said, referring to The Greenhouse's oversized toll house cookies.

A similar trial period last spring was unsuccessful, Burns said, because sunny weather discouraged students from going indoors to get a snack. But Burns decided to give evening hours a second chance this fall.