The lingering uncertainly over who will participate in the first presidential debate may be vexing for Jimmy Carter, Ronald Reagan, John Anderson and their political strategists, but here in the city that plans to host the kickoff debate, the concerns go far beyond politics.

For Baltimore, the aging port city that appears determined to become as major league as its baseball team, hosting the first debate is an unparalleled public relations plum.

It means 3,000 visitors, 1,500 reporters milling about in search of stories, half a million dollars in tourism and a chance to be viewed by a TV audience of 70 million Americans.

Officials here sought the number one spot with a scrappy vigor that has come to characterize their drive to boost the city's national image.

The league of Women Voters, which sponsors the debates, selected Baltimore in July as one of several prospective debate cities. When they came here, Mayor William Donald Schaefer, the city's chief booster, told the league officials: "We'll do the best job that'll be done by any city, and we won't consider the second or third debates. Or the vice presidential debate. We'll go for the first."

The mayor then arranged for a grand tour of the city, its redeveloping inner harbor and its new $50 million convention center. "Mayor Schaefer said everything we wanted, we could have," said Lee Hanna, director of the 1980 presidential debates. Baltimore won out, he said, largely because the League was convinced that "they had an exciting and interesting story to tell."

Ever since, Baltimore officials have been mobilizing resources to get that story out during the debates. Reporters will be treated like visiting royalty. Automobile dealers have volunteered dozens of cars, and local Jaycees have supplied plenty of drivers who will greet reporters as they arrive here by plane or train, according to convention center executive director James Smither.

Drivers will be equipped with information packets about the city, its history and its inner city revitalization program -- fodder for future news articles. Yachts will be on call to take reporters around the harbor and the public library has been put on alert to supply research material within minutes to any reporter who calls, Smither said. Hostesses with two-way radios will be stationed in hotels to call for drivers if a reporter wants to go sightseeing.

"If Walter Cronkite wanted to take the Pride of Baltimore out sailing, we could arrange it," Smither said. "We've thought of everything we can."

Civic leaders raised $150,000 to pay for frills including an outdoor banquet with all-Maryland fare -- chicken, oysters, shrimp and crabs -- for 1,500 reporters expected to come from Europe, Mexico, Canada and cities across the United States. The city has arranged for several league officials to stay in local hotels for free, and has mde the convention center available at no cost -- an in-kind contribution of $22,000, officials estimated.

The outpouring of resources prompted a federal lawsuit by Libertarian Party candidate Ed Clark, who alleged that the city was using public funds improperly for an event that would damage his presidential chances, since he was not to be included in the debate.

The city answered the allegation yesterday in court papers that testified to the value local officials put on their role as debate hosts.

Television coverage on the debates, with periodic shots of Baltimore scenes, "would be worth upwards of $2 to $3 million if purchased at present rates," the court paper said. "Total value of the worldwide coverage is so great as to defy accurate estimation."

As such, the city argued, there will be no net expenditure of public funds. The provision of free hotel rooms is routine, officials said, any time a convention brings in thousands of bookings.

"Cities like San Francisco, Las Vegas, they could care less about something like this," Smither said. "They are established convention cities. sBaltimore isn't and we know that. We're still emerging. The value of something like this is tremendous, and I mean tremendous."

With those hopes in the balance, recent indications that President Carter might not participate in the Baltimore debate -- thereby gutting its publicity value -- sent a shudder through several city officials.

Carter had said he wanted a one-on-one confrontation with Reagan in the first debate, but the league said that if Anderson's support reaches 15 percent in the polls by next Wednesday, he will be invited.

Yesterday, Baltimore's number-one spot and the president's participation began to look a little more definite. Carter's son, Chip, toured Baltimore with Schaefer and said it appears likely that his father will participate in the Baltimore debate, tentatively scheduled for Sept. 21.