"Mostly I leave New Yorkers because I hate to throw them away," said another Red Line user, adding that she did not use the library because "other people might not have anything to read, while I always have New Yorkers."

Other passengers said they like to donate books that they no longer need or that they want others to read. They said they would rather leave them on the Porter Square shelf instead of throwing them out or giving them to friends. Brown said one young man who brought 13 boxes of paperbacks to his office for the program.

The program does not have universal appeal. "I don't read. I watch T.V.," said one elderly man. "At least I didn't tell you I can't read," he added.

Despite Brown's efforts to provide a varied selection of books, many passengers complained that all they ever find on the shelves are romances and mystery novels. One commuter described the service as "a trashcan for people's old books."

Brown said he did not know how many of the books actually came back, but guessed that readers returned "at least 50 percent." But because of the many donations, he said theft was not a problem.

And plans are already under way to expand the program. Robert Dugan, a commissioner involved in the project, said that of the 270 grants his organization examined, "this is the one we keep talking about." He said he would be happy to consider expanding the program in Cambridge or even as far as Boston.

Brown said he hoped to put another shelf in Somerville's Davis Square station, and eventually to put a staffed kiosk in the Porter Square station. But he said Harvard Square was not likely to get a shelf because it would be hard to stock such a busy station.