COLUMBUS, Ohio — Poll workers will not be allowed to take voting machines home for safekeeping in the days before the November presidential election because the practice known as “sleepovers” is an unacceptable security risk, the state elections chief said yesterday.

Taking machines home makes it nearly impossible to keep track of what happens to a machine or memory card once it goes into the custody of a poll worker, Secretary of State Jennifer Brunner said.

The changes are meant to address actual security concerns — including the fear that machines could be tampered with — and national perceptions of Ohio’s election system, which has come under fire in recent years, Ms. Brunner said.

“We want Ohio’s voters and the rest of the nation to see that we have prepared a transparent process of transporting voting equipment, ballots and supplies,” Ms. Brunner said in a statement.

Ms. Brunner was elected in 2006 with a promise to improve a system marred by scattered problems of long lines and poorly trained poll workers.

Twenty-four of Ohio’s 88 counties have used sleepovers. Local elections officials argued that the practice makes it easier to take machines to polling sites. Otherwise, they would have to hire moving companies to distribute the machines at a cost of thousands of dollars.