"Phone Bank" says a sign in the lobby of the Amalgamated Clothing and Textile Workers building here in Cleveland. An arrow points to a stairway leading to the basement. In the basement sit a score of people who are probably going to be decisive in the presidential election.

Ted Kravinus is one of them. A retired communications worker. Gray haired and bespectacled. A pleasant manner.

In front of him is a phone. Beside the phone is a computer printout supplied by AFL-CIO headquarters in Washington. The printout lists the names, addresses and phone numbers of all union members known to be registered Democrats in Cuyahoga County, which embraces Cleveland and its nearby suburbs.

Name by name, Kravinus goes down the list. He makes a call, identifies himself, reads out the list of candidates endorsed by the union and then asks for a vote next Tuesday. He marks down the response favorable will be visited on Election Day by other union members and reminded to vote. If the record shows they have not voted by noon, they will be visited a second time. If theyhave not voted by four in the afternoon, there will be another visit.

Not all the response to the phone cals are favorable. "I don't want to hear it," one person said when Kravinus mentioned President Carter, whose name heads the list.

Parama, a white ethnic suburb west of Cleveland, is particularly difficult.

"Two big auto plants there," Kravinus says, "are down. They're paying much less in local taxes. The real estate taxes are going way up. That makes people mad at whoever is in power."

But on the whole Kravinus says he has never found a more "receptive climate" for phone bank operations. "It's easy to get hold of people," he says, and then he explains:

"The average union person thinks the Democratic Party is a friend in need. They may not understand why we're so strong for Carter. I say, "Look at the choice.' They know about Reagan and he scares them. Sometimes they say, 'He should go back to the movies.'"

Before Election Day, Kravinus and his colleagues in the phone bank here will have made 60,000 phone calls. There will be 18 union offices open in Cuyahoga County on Election Day to Help get out the vote. About 250 union members will be knocking on doors.

Warren Smith, the secretary-treasurer of the Ohio AFL-CIO, has set up similar phone banks in every industrial center in the state. He showed me the Cleveland operation, which he believes is working well. Another we visited, in Warren, a steel town to the southeast, also seemed to be functioning effectively.

But in Youngstown, another steel center with heavy unemployment, there was obvious trouble. The biggest union in town, the Steelworkers, had not made money available for the local Democratic candidate for Congress, nor assigned people to man the phone bank. "Not per se," a local union official said when I asked him whether the Steelworkers were playing a role in the presidential election. "We'll have to fix that," Secretary-Treasurer Smith said as we drove away.

Smith has been working Ohio politically for more than 15 years, chiefly as a lobbyist in Columbus. He's been into phone banks and precinct operations since 1975. This is his view of the presidential race:

"Carter won Ohio in 1976 with the rural vote in the southern counties. He won't do that this year. The novelty is over, and the grain embargo hurt.

"This time he'll have to win in Cuyahoga County, and the other industrial centers. We can do it. Reagan isn't that far in front. The margins are narrow. If we turn out our vote, we can carry Ohio."

I think he is right -- and not only about Ohio. The other big industrial states around the Great Lakes -- Illinois, Michigan, Pennsylvania, New York -- are also winnable for Carter. If he adds to them either Texas or Florida, the election is his.

Whether that will happen is not clear. The debate can change everything, as can the hostages. But if Carter does win, the key element won't be his personality or his record or his media advertising. It will be the Democratic Party, and the one remnant of that party with a presence on the ground Election Day -- organized labor.