Election officials and law enforcement agencies across the region are putting in place contingency plans to deal with any sudden spike in terror warnings over the next three weeks or the possibility of attacks at polling places on Election Day.

In a memo sent yesterday to each local registrar, Virginia's top election official urged a "delicate balance" between enhancing security to prevent terrorism and the need to avoid intimidating voters with an unnecessary show of force at the polls. Some registrars have opted for visible security changes, including placing uniformed police at polling places. Others are playing down the threat for fear of scaring voters and poll workers.

The schism underscores the difficulty officials are having in balancing voting rights against the uncertain but well-publicized warning that terrorists might try to disrupt the nation's Nov. 2 presidential election. Civil liberties advocates warn that too heavy a police presence might violate federal law.

U.S. Department of Homeland Security officials have warned of a vague election threat. Last month, the National Governors Association, in consultation with Homeland Security, sent a bulletin to the 50 states and the District that contained Election Day guidelines for coordinating police, tips for ballot-counting security and legal advice about ordering emergency election changes. But they offered no specific guidance and, for the most part, left it up to each municipality and county across the country to decide how to act. "State and local elections are administered under state and local law," said Brian Roehrkasse, a spokesman for Homeland Security.

In Maryland, officials said they are reviewing emergency procedures and stepping up police patrols. Montgomery County police said they are still considering whether to station officers at polling places. District officials said they have requested "upgraded support" from the D.C. police department for the election.

Election officials in Chesterfield County, near Richmond, have already decided to post an armed police officer at each of the county's 62 polling places for all of Election Day. The registrar there, a 16-year veteran of the Richmond Police Department, said concerns about intimidation pale in the face of terrorism.

"It's the way things are now. It's regrettable, but I think it's how we have to act," said General Registrar Lawrence C. Haake III. "We're in such a world now that either we've got to be prepared for anything or suffer the consequences of failing to prepare."

Prince William County officers will roam close to polling places, dropping in to check for suspicious cars. They also are training precinct workers to spot danger signs, officials said.

Registrar Betty Weimer said Prince William police will be posted at voting locations only if the nation's terror alert is raised or if terrorist "chatter" gathered by intelligence agencies indicates a more direct threat.

But other local governments have firmly rejected having visible signs of enhanced security and say people probably will notice no difference when they vote.

Maggi Luca, secretary of the Electoral Board in Fairfax County, said the county's security efforts will be invisible. She declined to elaborate, but she said Haake's decision to post uniformed officers at the polls was wrong.

"I don't want voters to be frightened," Luca said. "Can you imagine how intimidating that would be? We're not doing that."

Civil liberties groups and minority organizations across the nation have also expressed concern that a higher police presence at voting places could stifle turnout.

In 2000, black voters in Florida complained that police checkpoints scared some from casting ballots in the very close election. The charges brought back echoes from the nation's civil rights history, when government power was used throughout the South to turn away black voters.

"There's no question that if you were to put police officers and sheriff's deputies at the polling places, it would have an intimidating effect," said Laughlin McDonald, director of the American Civil Liberties Union voting rights project. "There are thousands of precincts around the United States. We can't make them armed guardhouses."

In Maryland, Gov. Robert L. Ehrlich (R) said the state is discussing security with federal authorities. "It's clear to everyone that Election Day 2004 is going to be quite different because of 9/11," he said.

Virginia's homeland security officials said they have discussed with registrars and police the need to balance access and security. "We have to have that absolute right balance, right in the middle," said George Foresman, security chief for Gov. Mark R. Warner (D).

Virginia officials also have urged local registrars, police departments, sheriff's offices and others to be ready to act swiftly in the event of an attack before or during Election Day that might interfere with voting.

Many registrars said they have for the first time developed detailed lists of alternative polling places. In Fairfax, each of the 220 precincts will have two alternatives "in opposite directions," said election manager Judy Flaig.

In Prince William, officials have had to make specific plans for a polling place on the Quantico Marine Base. If the nation's alert level rises, access to the base could be cut, leaving a precinct without a place to vote.

In Norfolk, election officials have decided to use their library bookmobile as a portable polling place, if necessary. In Fairfax, officials said they have made arrangements to use a special county bus for the same purpose.

Officials said they also have revamped their Election Day communications with poll workers in case a terrorist attack requires rapid notification to many precincts simultaneously.

In Fairfax, officials say they have implemented a secure instant message system that can broadcast text messages to thousands of pagers and cell phones. Poll workers who do not have personal cell phones will be given one, county officials said, and workers at polling places where cellular signals are weak will be given pagers.

State election officials in Virginia and Maryland said they will have the capability to move personnel and data to backup locations if their offices are unusable.

"All the mechanics are in place," said Virginia Secretary of the Electoral Board Jean Jensen.

Staff writers Phuong Ly, Matthew Mosk and John Wagner contributed to this report.