Thomasina Allen, who heads the New Theatre of Washington, a small musical theater company located in the Lansburgh building, pleaded guilty yesterday to a charge of writing a $25,000 bad check and was sentenced to six weeks' imprisonment.

U.S. District Judge Barrington D. Parker sentenced her to 30 months, but suspended all but the six weeks, "considering your background and the fact that you're a lady." He also put her on probation for three years. She could have been sentenced to as much as 10 years.

Allen, whose New Theatre received a $15,000 "institution building" grant this year from the D.C. Commission on the Arts, was charged under a plea-bargain arrangement with the U.S. Attorney's Office with writing a fraudulent check on a Chicago bank account she set up under a false name.

Harry T. Alexander, Allen's attorney, said in court that she showed bad business judgment rather than intent to defraud, and enumerated her achievements in the arts and her contribution to the community. He said later that he has filed a motion asking Parker to reconsider the jail sentence and perhaps to substitute community service, on the grounds that "people who have committed far more heinous things are still walking the streets. This woman is not a criminal type. She has a problem of talking too much, she is not a con artist. She served a penance and a sentence in that courtroom this morning."

Alexander noted that Allen had letters of support from seven people, including City Council member H.R. Crawford and D.C. Del. Walter E. Fauntroy, and that she has graduate and undergraduate degrees in music and music education. Five years ago she produced a musical performed by children, "The Trees Talk Back," which played in city parks.

The New Theatre of Washington and the adjunct New Theatre School are are both still operating, according to Alexander, although the listed telephone has been disconnected. The New Theatre of Washington was originally the name given to the first descendant of the old Washington Theater Club when it merged in 1973 with a theater managed by Allen's former husband, Paul Allen. It subsequently produced shows in other places around town, and changed its focus from theater to musical theater, opera and children's theater. Paul Allen has since moved to Cleveland.

Thomasina Allen has also received grants from the National Endowment for the Humanities and the Hattie M. Strong Foundation.