A Potomac River cruise and a benefit performance at the Little Theater of Alexandria were scenes last week of the first major fundraising in the race for state senator from the 30th District, which covers Alexandria and parts of Fairfax County.

On Wednesday evening, approximately 200 persons paid $10 apiece to see the theater's production of the musical "Fanny," with proceeds going to the campaign of Democratic candidate Beverly Beidler, a two-term member of the Alexandria City Council in the 1970s.

More than 90 persons paid another $25 to be listed as patrons of Beidler's campaign, among them Alexandria Mayor Charles Beatley and Dels. Marian Van Landingham and Bernie Cohen. Before the curtain rose, a car drew up bearing guest of honor, Lt. Governor Richard Davis.

The function netted about $3,500 for Beidler, who is attempting to unseat two-term Republican incumbant Wylie Mitchell.

Two days after Beidler's function, Mitchell hosted 220 persons for a charter cruise from Alexandria's torpedo plant pier to Mt. Vernon and back. Guests paid $75 for a single admission or $125 for a couple and were entertained by a Dixieland jazz band. The cruise netted about $7,000.

Among those present at the function were Alexandria Councilwoman Margaret Inman, Republican National Committee Chairman Frank J. Fahrenkopf and Del. Frank Medico.

Mitchell this week opened a campaign headquarters on North St. Asaph's Street in Old Town.

A spokesman for Beidler's campaign said she has no plans to open a campaign office but plans to take part in any joint Democratic campaign center that is formed.