A reunion of the American Light Opera Company has been scheduled for April 1 at the National Theatre following its regular Monday night program. Anyone who worked with the company is invited; there will be a cash bar. The company was a group of enthusiastic amateurs that operated between 1960 to 1966, before there was much professional theater activity here, performing musical comedies at Trinity Theater and Cramton Auditorium. Sometimes it took shows on the road to the Lyric Theater in Baltimore and once to the Mosque in Richmond. Organizers are radio announcer Ed Merritt and National Theatre president Donn Murphy, who has made the theater's 24-hour line available for reservations: 783-6854 . . .

Rebecca Rice and Janet Stanford's "This Is the House" will be performed tonight at the New Playwrights' Theatre as a benefit for My Sister's Place, a shelter for battered wives in Northeast Washington. The play, not surprisingly, is about a battered wife. Call 832-9563 or 232-1122 . . .

Arena Stage is having its annual benefit this Saturday. It's called "An Evening of Unpremeditated Mirth" and features the comedy team of Monteith and Rand. The theater hopes to raise $50,000 for operating expenses from the select 400 who are to attend . . .

Auditions for a summer scholarship to the Birmingham Summer Fest are being sponsored by the Friends of the Kennedy Center this Sunday at 2:30 p.m. They are open to young people 18 and older. Be prepared with one ballad and one up-tempo song, and bring your own music; an accompanist will be provided. The scholarship includes air fare, housing, spending money and roles in three musicals. Go to the stage door of the Opera House. Call 254-8700.