The Harvard Square Development Task Force has scheduled an open meeting for 8 p.m. tonight at the Martin Luther King School to invite community discussion of proposed plans for the Kennedy Memorial Library.

Oliver Brooks, chairman of the Task Force, said yesterday that there would be three major items on the agenda:

* Presentation of the third option for use of the related facilities area, a hotel-motel with 400 units and parking space for 750 cars above and below ground (two earlier options were an open parking lot and residential condominiums);

* Discussion of the preliminary "scope of work" statement for the environmental impact study to be conducted by the Federal government;

* Comments and questions from community residents about any aspect of the Library and its effect on Cambridge.

Several members of the Task Force, the major community group reviewing plans for the entire project, have privately expressed disappointment over the preliminary scope statement released to them last week.

They say it treats the Library as an organic whole, instead of the sum of individual parts such as the archives, the museum, Commonwealth Plaza, the related facilities area, and the John F. Kennedy School of Government.

Some members have also complained that the statement ignores the potential impact of the Library on the surrounding communities of Cambridgeport, Riverside and West Cambridge.

Asked if she detected any signs among local groups of a momentum building against the Library as presently planned, one member of the Task Force, Sally von Henneberg, replied last night, "I would say that there are quite a lot of unanswered questions about the Library that are bothering a very large section of the community."