Nearly one out of four Marylanders who have tried to register to vote at a Motor Vehicle Administration office in the past four years has not been added to the voter rolls, according to state records obtained by The Sun.

Though some of these tens of thousands of would-be voters have undoubtedly found alternative methods to register, officials at the State Board of Elections say they field calls every year from residents who say they turned up at the polls on Election Day only to discover their names did not appear on the rolls.

Elections officials, good-government advocates and lawmakers say the failures illustrate the challenges of implementing the federal Motor Voter Act.

The 1993 law, which requires states to offer voter registration to citizens when they apply for driver's licenses, was intended to expand the voter rolls and increase participation in elections. And there has been progress: The MVA has helped sign up 451,386 new voters since January 2007.

But critics say it has burdened motor vehicle departments with an unfamiliar responsibility.

"Their primary focus is not elections," said Del. Jon S. Cardin. "We have required them to take this on."

Nonetheless, the Baltimore County Democrat calls the failure rate "a grave concern." He is one of several lawmakers pushing for improvements.

"We cannot be satisfied with one-fourth of the people who want to vote not being signed up," he said.

State Board of Elections records requested by The Sun show that 144,442 would-be voters started the registration process at an MVA office during the past four years, but for some reason, their names did not get on the voter rolls.

The number would not have made a difference in the lopsided victory of Democratic Gov. Martin O'Malley last fall over former Republican Gov. Robert L. Ehrlich Jr., but it is significantly larger than the margin that separated them in 2006 — though none of them would have been registered in any case in 2006.

The state elections board denied a request by The Sun for the names of people who tried to register. Officials did provide The Sun with a geographical breakdown of the failures, which showed that a disproportionate number come from Baltimore City and Prince George's County.

Baltimore, home to 10.8 percent of the state's population, had 13.2 percent of the failures. Prince George's, home to 15 percent of the population, saw 18.1 percent of the failures.

An MVA spokesman blamed the bulk of the problem on the applicants, who he said often tell clerks that they want to register to vote, but then fail to follow through by signing and returning the necessary forms.

"We offer the opportunity to start the process," spokesman Buel C. Young said. "We do what we're federally required to do under the motor voter law."

Elections officials are not satisfied.

"It is just not a good system," said Mary Wagner, the state's director of voter registration. "There are human hands involved. I'm sure that between the applicant and clerks at the MVA, papers get lost."

Though many states have struggled to implement the motor voter rules efficiently, Maryland's experience stands out.

"That problem is of a scale that is off the charts," said Adam Skaggs, an attorney who focuses on election administration for the Brennan Center for Justice at the New York University School of Law. "Twenty-five percent trying to register and having their registration lost, or not processed? That is absolutely unacceptable."

The problems are not limited to voter registration, according to elections records.