For today at least, Baltimore became two cities -- one, the polished stage for the first of the presidential debates; the other, a blend of rubble and renovation, little different from others around the country.

From the southern outskirts of the city on in, almost every street corner showed the changes wrought for the day of the debate: new signs pointing the way to the city's prize attractions and new pennants across the streets bidding visitors a hardy welcome from the town's irrepressible impressario and mayor, William Donald Schaefer.

But five blocks away from Baltimore's cavernous convention center, the site of the debate between Ronald Reagan and John Anderson, the residents of the city's poverty-ridden inner neighborhoods didn't really see the point of the whole thing.

"I'm going to be truthful with you, I don't even know what's going on with them political peoples," said Beaver Jones, 23, a west Baltimore resident. "I don't think nothin' about it, there's too much scandal about politics. I ain't even voted for the last four years," said Anthony Buleigh, as he leaned on a wall near two newpaper boxes advertising "Baltimore's great debate."

In a way, the gulf between the two Baltimores was symptomatic of the mixed feelings that surrounded the debate: some people showed great excitement about hosting a presidential debate, even one that was lacking a president, while others, exasperated by politics, just didn't care.

For Mayor Schaefer, however, nothing would spoil the magic of this moment which brought his city into the spotlight -- not the absence of President Carter, not the talk about record job lines and high unemployment, not the low and late turnout of the representatives of the national media whom he wanted to impress.

"I am way beyond my expectations," he bubbled as he left a cocktail party -- one of many thrown for the press and assorted city and national VIPs -- at Harborplace, the city's glistening new showcase. "Our people have just been super. The more good will you spread, the more people some day may say, 'I know a super place where we ought to have our convention.'"

Schaefer, who raised $200,000 from local businesses and banks to spend on the logistics, facelifting and festivities surrounding the debate and assigned 800 city policemen to keeping order, said he made no attempt to persuade Carter to participate even though he knew the president's absence would deflate the publicity value of the debate.

However, the mayor, a long-time Carter supporter, did see fit to intervene with the League of Women Voters -- the sponsors of the debate -- to dissuade them from placing an empty chair on the platform to dramatize Carter's absence.

"That's a personal thing," the mayor said. "I just don't like to embarass anyone. We're not trying to do anything negative. We're trying to show a city where everyone is welcome.

Schaefer was not the only one who chose to use the forum provided by the debate as a bulletin board for his message. But while he chose to show off the city and its people to anyone who would pay attention, an unlikely assortment of political action groups sought instead to promote their various ideologies.

The most valuable group among those who converged on the covention center tonight was a coalition of the Communist Workers Party and the Baltimore Welfare Rights Organization. Together, 70 members of the two groups marched several blocks through downtown, gesticulating and yelling through bullhorns, "Lying politicians, it's payback time."

Police arrested thre demonstrators, shortly after stopping a van that was following the group the wrong way down the major one-way thoroughfare of Pratt Street. The driver of the van, who identified himself as Robert Duncan of Washington, was dragged out of the vehicle, handcuffed and charged with a traffic violation.

The women demonstrators were also arrested and handcuffed, although police on the scene were vague as to the charges on which they had been arrested.

The 10-minute fracas occurred just as a half dozen other demonstrations -- including rallies for the ERA, against nuclear power, against the draft, for a group of dissident GIs and for jobs, equality and peace -- were winding down.

At least two of the the demonstrations focused on the city's umemployment picture, dramatized last week by the turnout of more than 26,000 men and women who picked up applications for 70 unskilled jobs at the Social Security Administration here.

But in a conversation at a predebate reception, Schaefer sought to downplay this phenomenon, saying it was "magnified by the press."

". . . There are still thousands of jobs (listed) in the papers that people either aren't qualified for or don't want," he said. He said, a little annoyed that the subject of umemployment should come up on a day when he was being so insistently optimistic about his city.

"Social Security is a nice place to work," he said.

Demonstrations, of whatever kind, were the least of Jim Smither's concerns. The Baltimore Convention Center's executive director, walkie-talkie in hand, was still trying to cope with the logistical essentials of this great undertaking today: essentials like press passes, sound systems, tickets, nurses and chairs.

The chairs had for several days been one of his most intractable problems.

One configuration had been planned on by convention center officials, another requested by the Secret Service, and another by the candidates. Then the TV technicians had their problems with the whole business, and the Secret Service people decided to change their mind about what they wanted.

Then, yesterday, morning, the city's fire marshal said the Winnebagos had to go.

The large vans, one for each candidate to relax and prepare in, had been set up behind the royal blue curtains that served as a backdrop to the debate platform. But suspicious fire marshals had discovered that the Winnebagos were equipped with propane gas tanks. And propane inside a building, in Baltimore is something they won't allow.

"We moved out the Winnebagos Saturday morning. Then we had to pull the curtains back, pull the chairs up and rearrange again," explained Wayne Chappell, who works with Smither on the convention center staff.

That was a few hours before the advancemen for the two candidates agreed that about 100 chairs in the front of the hall were too close to their men for comfort. "The man on stage is thinking. He doesn't want distraction," Smither said. So one central block of chairs was eliminated and the configuration of the hall had to be rejiggered again.

"The candidates have needs, the Secret Service has needs, the audio and lighting people have needs, we have needs, the League of Women's voters has needs. We're just keeping everyone happy," said Smither. "It isn't hard -- we're all pros."

While Baltimore officials took care to make sure that no details were overlooked, the League also took even the most minor matters seriously. After wrestling for days with angry politicians over the question of who should get how many of the 2,600 tickets to the debate, they then had to face the coin toss.

The ceremonial toss to decide which candidate would go first in responding to the panel of questioners was duly performed late yesterday afternoon.

Political consultant David Garth called heads on behalf of Anderson, campaign official Jim Baker called tails on behalf of Reagan. Anderson won. But, at the League's urging, it was no run-of-the-mill coin that was tossed. It was instead of a Susan B. Anthony dollar, bearing the image of the leading 19th century women's rights leader.