Alexandria Sheriff Michael E. Norris said yesterday he will seek the Republican nomination for delegate to the General Assembly from the city's 21st District.

Norris said his decision followed the announcements in recent days by Alexandria's two incumbent delegates, Republican Gary R. Myers and Democrat Richard R. G. Hobson, that neither would be a candidate for reelection.

Norris, 30, was elected sheriff in 1977 following the resignation of Sheriff Raymond Foge. The sheriff's office is responsible for prisoners, serving legal documents and courthouse security.

Another Alexandrian who had been expected to seek the Republican nomination for delegate, deputy city attorney Burton B. Hanbury Jr., said yesterday that he has decided not to run.

Hanbury, 33, next week will join the Alexandria law firm of Wrape, Hernly, Booker, and Swersky, which represents, among other clients, the Alexcom corporation, one of three firms seeking a cable TV franchise in the city. Hanbury was one of the principal authors of the city's cable TV ordinance.

Hanbury said yesterday he would participate in Alexcom's legal matters "only if and when Alexcom gets the franchise."

Myers and Hobson both cited financial concerns as their reason for not running again.The position pays $5,400 annually. Norris, who currently earns $28,000 annually, said he will enter private business if elected. The last day for candidates to file is April 13. The primary is June 12.