Florida Gov. Reuben Askew selected Janet Reno, Harvard Law School '63, to head the Dade County Attorney's Office in Miami, Fla. yesterday, making her the first woman to head the jurisdiction with the largest office staff in the South.

Present State Attorney Richard Gerstein announced his retirement last March, and for the past six months Askew has been looking for a replacement.

Miami's high crime rate has increased the office staff to 315, including 105 lawyers.

"The Governor studied the suggested candidates and made contacts. From the contacts, Janet was the near unanimous choice," Morris Harling, special assistant to Governor Askew, said yesterday.

As administrative assistant to Gerstein, Reno has had only limited criminal trial experience but she does not feel it will affect her job performance.

"The job is largely an administrative one. With all the responsibilities within the jurisdiction, a state attorney has no time to try cases," she said yesterday.

The next election for the Miami office position will be held in the fall. Barry Kuten, a member of the Florida state legislature and a personal friend of Reno, is considering challenging her.

"When Gerstein announced his retirement last March, I wrote the Governor to let him know I was interested, Kuten said yesterday.

Kuten said that he feels he has had adequate experience in serving the public in an elective office and that the voters know where he stands on the issues.

Reno will run to maintain her position, but she also has other objectives. "I would like to develop a highly professional staff and close relationships with the local law enforcement agencies in Dade County."