The 137 to 0 vote in the House and the endorsement of the plan this week by Republican Gov. Robert L. Ehrlich Jr. represents a stunning turnaround for a state that was on the leading edge of touch-screen voting in 2001, and it reflects a national shift toward machines that provide a paper record.

The touch-screen system, for which Maryland has committed more than $90 million, would be put aside for one year while the state spends at least $13 million to lease optical scan machines.

"It's critically important for voters to know their vote was cast and that it will be counted correctly," said Del. Obie Patterson (D-Prince George's).

The fate of the plan in the Senate is less certain, and Ehrlich has not set aside money in his budget to lease the new machines. Senate President Thomas V. Mike Miller Jr. (D-Calvert) yesterday defended the record of the state's touch-screen machines and said that changing systems six months before an election would cause headaches for local administrators and lead to long lines and late returns.

In a sign that the Senate is moving in a different direction, Sen. Paula C. Hollinger (D-Baltimore County) has arranged for Diebold Election Systems to demonstrate for lawmakers today a newer version of its touch-screen machine that provides a paper receipt. Maryland's model is not compatible with any existing printers.

The uncertainty leaves election administrators in limbo as they prepare for the September primary. Such preparations typically take 12 to 18 months, but Montgomery County elections director Margaret Jurgensen predicted that administrators would have perhaps 60 to 90 days. If the state abandons the touch-screen machines for this election, it would be the third voting system for Montgomery residents since 2000.

"I can either laugh hysterically or cry," Jurgensen said. "With all these things up in the air, no one can make a move. We don't know if we need phone lines at polling places or to spend money to hire 65 armored cars to pick up ballots on Election Day."

Maryland's struggle over how voters should cast ballots is part of a national debate on the reliability of electronic machines, which critics contend can be corrupted by computer hackers to affect the outcome of elections.

In the wake of the 2000 presidential election, Maryland was one of three states -- along with Georgia and Florida -- that moved quickly to embrace electronic machines.

More than two dozen states now require some form of vote verification. In New Mexico, the governor signed legislation this month to switch to optical scan-style voting statewide, including in four counties that have spent a total of $4 million for touch-screen machines.

Georgia's secretary of state, a longtime proponent of her state's paperless touch-screen system, has recently endorsed a pilot program to put electronic machines with a paper trail in a limited number of polling places -- a plan that could become a model for Maryland.

Virginia and the District use a mix of touch-screen and paper ballots. Legislation to require a paper trail in Virginia failed this session.

Dan Seligson, editor of Electionline.org, a nonpartisan group that monitors election reforms, said the critical issue in every state is voter confidence that can be eroded by a good public relations campaign against the electronic machines.

"Once word gets out that there is concern over the lack of paper, that begins to spread," Seligson said. "Whether or not the machines are less secure than they were before the campaign started is another story."

Questions were raised in 2003 about Maryland's Diebold machines after Johns Hopkins University computer security experts found that the software could be easily hacked.

The push for paper -- backed by the small but vocal Takoma Park-based group TrueVoteMD -- gained new strength last month when Ehrlich announced he had lost confidence in the state Board of Elections' ability to conduct accurate elections. The governor, who had been a champion of the Diebold machines, also called for a paper trail for the first time.

Maryland's top elections official, Linda H. Lamone, has characterized the proposed switch as a step backward and said paper provides a "false sense of security." Lamone and Board of Elections Chairman Gilles W. Burger have said that an optical scan system, which relies on hand-marked ballots, can leave questions about whom the voters intended to choose and can create printing problems.

John T. Willis, the former secretary of state who pressed for the current system, said the legislative proposal would be worse than any perceived problems.

"There is no evidence of anything wrong with Maryland elections," he said, citing a study by the California Institute of Technology and the Massachusetts Institute of Technology showing that Maryland had the lowest rate of voter error in the nation in 2004. "It's a very distressing way to do public policy."

Miller and other Democratic leaders have said that the governor's position on the state's voting system is based on politics and his opposition to plans for early voting. In January, the General Assembly overrode Ehrlich's veto of a bill to allow voting at some polling places five days before an election. In February, Ehrlich wrote the elections board chairman saying that concerns about the security of voting machines would be exacerbated in Maryland because of early voting.

Staff writer Yolanda Woodlee contributed to this report.