It may be the biggest event to hit Fairfax City since Mosby's Raiders attacked the local courthouse to free Confederate prisoners.

News that a president of the United States, a geographic neighbor but an exceedingly rare visitor to the Virginia suburbs, will appear in person there Thursday night has started a scramble that has ticket distributors wincing and ticketless citizens maneuvering to get in.

The problem arises from President Carter's scheduled appearance at the 400-seat Fairfax High School cafeteria to participate in a roundtable discussion of his proposals for civil service reorganization. Forty percent of the more than 300,000 households in the 10th Congressional District, which includes Fairfax City, have at least one civil service employe living there.

The White House which said it wanted a "manageable size group" for the event dispensed small blocks of tickets in advance to the Fairfax Chamber of Commerce, the League of Women Voters and other civic and political groups in the district - even the Republicans.

"I wish you wouldn't say I had any tickets." said Emillie Miller, chairman of the Fairfax County Democratic Committee, who said she had been besieged by people seeking admission. She is giving her 10 tickets to committee members who she thinks are interested in civil service reorganization.

"I didn't rate any more tickets than the Republican did," she noted, adding that she was unhappy about that "enemy" being included.

Judy Shreve, chairman of the 10th District Republican Committee, said two of her tickets went to the senatorial campaign of Richard D. Obenshain and eight to the congressional campaign of Frank Wolf.

Wolf is seeking to unself 10th District Democratic Rep. Joseph L. Fisher, who will participate in the roundtable with Carter.

White House spokeswoman Claudia Townsend said yesterday that Carter will open the appearance with a statement. Then he will join in a discussion with Fisher, Civil Service Commission Chairman Alan K. Campbell, Larry Suitors, a 10th District Republican, and seven other federal employes and community and civic leaders.

She said that the 400 observers might be allowed to ask questions if there is extra time at the session, which is scheduled to last one hour.

Townsend said the White House selected the 10th District because of Fisher's "interest" in civil service reorganization and the large number of civil servants who live and work in the area. Fisher has yet to announce whether he will support Carter's civil service proposals now pending before Congress.

Elected officials in the district automatically received coveted tickets. That included Fairfax City Mayor Frederick W. Silverthorne, who said he planned to attend although he regarded it "primarily a show by the president and his staff."

Silverthorne, who also was given a ticket for his wife, Betty, said he was relieved that he was not given tickets to distribute to others. "That way I'm out of the circuit," he said.

The "circuit" included some confusion about where tickets could be obtained. Callers to the Fairfax City government were referred to Fisher's office. But Fisher aides, who had few tickets to give out, passed the calls on to the individual civic groups.

That's when Pat Watt's phone began to ring.

Watt, who had only 10 tickets to distribute among the 600 members of her organization, the League of Women Voters, said she contacted a couple of federal workers and the spouses of other civil employes who she thought might be interested in attending, and could not give much help to others.

"It's a little bit arbitrary," she said, "but I'm trying to be fair."