After Harvard University officials detailed an ambitious plan last week to expand the university’s facilities into Allston over the next 50 years, the university has responded to criticisms from neighborhood groups that have raised concerns the plans will negatively affect city residents.

Though some Allston neighborhood groups worry the expansion will change the area’s character and reduce its affordability, Harvard spokeswoman Lauren Marshall said the new construction will not adversely affect housing availability for Allston residents even if more students moved into the city from across the river. Marshall said the plans are being developed to accommodate those students, and the university does not expect to significantly increase its number of undergraduates.

As of this school year, 98 percent of Harvard undergraduates and half of graduate students already live on campus, Marshall said. The expansion plans outline the creation of four undergraduate dorms in Allston and 590 graduate housing beds.

Harvard submitted a 74-page plan to the City of Boston last week outlining the first 20 years of a 50 year construction plan that would develop the area in the image of its existing Cambridge campus. Plans include the construction of new science facilities, relocating several graduate schools and museums — including the Peabody Museum and the Museums of Art and Natural History — and completely renovating the Barry’s Corner area into a retail and cultural destination similar to Harvard Square.

The plan calls for Harvard — which already has its business school and athletic facilities located in Allston – to break ground on the Allston Science Complex and the Harvard University Art Museums art center this year, Marshall said. If construction proceeds according to plan, she said those facilities will be completed by 2010.

The plan, which also aims to beautify the area, proposes improvements in transportation, including pedestrian walkways, bicycle lanes, new streets and grassy yards to replace current paved lots and overgrown sidewalks.

While Allston has earned a dubious reputation as a “grimy” city, supporters of Harvard’s expansion plan hope the university’s construction will increase the neighborhood’s appeal.

College of Arts and Sciences senior Sam Alter, who has lived in Allston for a year and a half, said he tries not to venture far into the city, calling it “nasty.” Alter said he looks forward to improvements in the area, and he said Boston University students will need better transportation for Harvard’s planned shops and restaurants to become a hot spot for college students.

Harvard plans to run four shuttles between Allston, Cambridge and the Longwood Medical Area, two of which may be open to the public.

“As of now, it’s just a tiny little crooked bus that goes there,” Alter said, adding he finds the walk down Brighton Avenue unpleasant. Rail yards and the Massachusetts Pike separate the westernmost edge of BU from the area, as well.

BU spokesman Colin Riley said the administration is working with Harvard, as well as city and state officials, to plan the expansion. He declined to comment on specifics, however, because the plans were only recently submitted.

Riley said the school anticipates more BU students will stay on campus — as opposed to finding off-campus housing in Allston — when Student Village 2 apartments are completed in 2009.

He said because the university’s goal for Student Village 2 is to offer housing to every BU student, he expects students will be less-inclined to move into Allston.

Julie Crommett, a Harvard junior, said Harvard students generally favor the expansion, although most will not benefit from it because it will not be completed until long after they graduate. She said students who move to Allston will able to take advantage of their proximity to Boston.

“I don’t know whether they’ll feel closer to the campus or the city,” she said.

CAS freshman Aubrey Podell, who said she has many friends at Boston College and the Massachusetts Institute of Technology because their campuses are close to BU, said she hopes the expansion will increase interaction between students from BU and Harvard.

“I think that uniting the academic communities is always a good idea,” she said.

“The whole ‘across the river’ thing is sort of a hindrance,” she said. “If we have the Harvard population sort of moved over to our side, I think there will definitely be more interaction.”