The finance committee of the D.C. Board of Education last night asked Superintendent Vincent E. Reed for an alternative to increasing class size in the elementary schools as a budget cutting device.

Reed has proposed increasing the pupil-teacher ratio from 26.1 to 28.1 in grades one through six to save $6 million in the 1981 budget, which goes into effect next Oct. 1.

The proposal for increasing class size was part of an overall plan Reed submitted to the finance committee last week for dealing with a $27 million deficit the school system is facing for the 1980-81 school year.

Other parts of the plan call for eliminating about 900 jobs -- 700 of them teaching positions -- reducing prekindergarten class from all day to half-day and cutting back on the system's administrative staff.

In a separate action, the school board's committee on educational assessment and development voted to eliminate the school system's six regional administrative offices to save $1.6 million. These offices were opened a few years ago to bring the system's central administration closer to the communities it serves.

Alaire B. Rieffel, chairman of that committee, said she will propose that the $1.6 million saved by closing the regional offices be used to keep more teachers in the system.

Reed said he does not know what alternatives to increasing classroom size he and his staff will present to the finance committee. Committee member Eugene Kinlow suggested that the superintendent consider possibly raising the price of school lunches by a nickel or tightening the regulations for employes' sick leave.Kinlow said it is common practice for employes to retire a year early by using all their accumulated sick leave.

Committee chairman John E. Warren scheduled a public hearing on the proposed budget cuts for April 26.