After weeks of stump speeches, radio and TV commercials and town hall forums in almost every corner of the state, the Pennsylvania showdown between Sens. Hillary Rodham Clinton and Barack Obama will come down to what happens at the polls tomorrow.

And the smoothness of what is shaping up to be a historic election with more than 8.3 million people registered to vote -- the highest number in this state's primary history, according to the Pennsylvania Department of State -- hinges on well-prepared voters and a coordinated balloting system, say county elections officials.

"My worry is the first-time voter who doesn't know what is expected of them, showing up at a polling place and expecting to vote," said Mark Wolosik, head of Allegheny County's Elections Division.

"They must have some form of identification; they must be registered either as Democrats or Republicans --Independents can't vote -- and they must know their polling stations," he said.

Still, he said, in an election that is expected to have an especially high voter turnout, some people may not follow the rules. They will show up without voter registration cards, identification or even at the wrong polling place.

For many of them, it will be too late.

"Find out what you need to know before you get to the polls," Mr. Wolosik said. The Pennsylvania Department of State has compiled a basic rundown of all the information a registered voter needs to be eligible to cast a vote tomorrow.

New voters who registered as Democrats or Republicans can use any of 15 acceptable photo and non-photo forms of identification, Mr. Wolosik said. They include a driver's license, U.S. passport, student ID, a firearm permit, a utility bill or a current bank statement.

For a comprehensive list of identification requirements and polling place locators, he added, voters can find the information they need on the county and Department of State Web sites: www.alleghenycounty.us/elect and www.votespa.com, respectively.

Beyond that, however, the county elections chief said his office is well-prepared to handle many of the election day maladies that have occurred in other states. His office, he said, is ready to deal with long lines at polling stations, and first-time voters who might need help, even though some voting rights groups already have raised concerns about the election.

Mr. Wolosik was one of six county elections supervisors in Pennsylvania who received a letter from a Washington, D.C.-based group this week, calling on him to ensure that trained election workers will implement emergency ballot procedures tomorrow, if necessary.

Kathryn Boockvar, a senior attorney, for the Advancement Project, a Washington, D.C., civil rights group, cautioned that since the mid-term elections in 2006, many counties and election officials have experienced "confusion, inadequate direction and inadequate preparation for what standards and procedures to follow should voting machines break down or malfunction."

Ms. Boockvar, who sent the same letter to elections supervisors in Berks, Chester, Lehigh, Northampton, and Philadelphia counties, cautioned that because of the importance of Pennsylvania in this election cycle, a lack of clear-cut emergency procedures could spell disaster.

Two national advocacy groups, Common Cause and Verified Voting Foundation, sounded a similar warning in a report released on Friday, noting that Pennsylvania's "paperless electronic voting machines have a history of unreliability, and voters and election officials should be prepared."

But in Allegheny County, Mr. Wolosik said his election workers are not only prepared for election day malfunctions, but they also have all been trained on provisional-ballot and voting-machine-breakdown procedures.

"We have very clear policies on what we are supposed to do and we are ready to act in case of an emergency," he said.

Final preparations for election day started on Wednesday when county officials conducted a full-scale test of the voting machines at a North Side warehouse.

"The ballots scanned perfectly," he said, adding that all 1,321 county polling stations received emergency paper ballots this weekend.

According to county regulations, each polling station will have at least 50 paper ballots per party, he said, that will be used only if all voting machines at a polling station break down and cannot be restored. If a polling station has to use paper ballots, it must revert to voting machines as soon as they are fixed.

And with more than 200 election workers in the field -- 56 zone custodians and more than 150 technical support staff "rovers" -- Mr. Wolosik said each polling station will have a supervisor that will notify and get clearance from the elections office before implementing any emergency procedures.

The county elections division also will run a "parallel test" tomorrow, Mr. Wolosik said. An accounting firm has selected three voting machines at random, and they will be used in a voting simulation tomorrow to test the accuracy of the real vote, he said.

But even with all the preparation for tomorrow's election, Mr. Wolosik knows to expect the unexpected.

"You can prepare as much as you want, but come election day, it's a different story," he said. "All we can do is be ready to handle whatever happens."