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The suit, filed in federal court in Virginia, seeks to have Mr. Buchanan declared the "properly nominated candidate." At stake in what could be a protracted court battle is which candidate will be on the ballot in numerous states, as well as which faction has the right to operate the party's Web site and issue its news releases.
The suing party, led by national Chairman Gerry Moan of Arizona, is asking for a temporary restraining order to halt efforts to list Dr. Hagelin on state ballots. A preliminary hearing is set for next Wednesday.
"They're running all over the country filing certification of nomination," Mr. Moan said, referring to the Hagelin Reform leaders.
New York lawyer Leonard A. Goldman said the Hagelin faction intends to answer with the "mirror image" of the Buchanan complaint.
"We will be asserting very strongly that the proper party is the one headed by Jim Mangia, and the procedures he followed for the convention were the proper procedures and therefore Dr. Hagelin is the candidate," Mr. Goldman said.
The party split two weeks ago in Long Beach, staging separate nominating conventions. Mr. Mangia of California was elected national chairman of the breakaway group, which nominated Dr. Hagelin, a leader of the Natural Law Party. Mr. Moan's group nominated Mr. Buchanan, a one-time Republican presidential candidate.
The Federal Elections Commission must resolve the question of which candidate should receive $12.5 million in federal funds, but first it must receive notification from 10 states that the party nominee is on the ballot. It has 10 days to rule once it receives the necessary paperwork.
Buchanan campaign attorney John Duffy expressed confidence that Mr. Buchanan, who won the party's primary and had a majority of convention delegates, will be awarded the funds.
"Time is of the essence," he said, adding that he expects the FEC to "work diligently to get us the money as soon as possible."
The FEC meets Thursday, but spokesman Ian Stirton said the timetable for a decision is uncertain.
"There are all kinds of questions," he said, "This has never come up before. What are you going to do? Divide the baby?"
Meanwhile, Dr. Hagelin said at a Los Angeles news conference that he will campaign regardless of the funding disbursement, with help from Nat Goldhaber, the millionaire high-tech entrepreneur who joined his ticket.
As for Mr. Buchanan, he's recuperating from surgery to remove his gall bladder and is expected to return to the campaign trail next week, a campaign aide said.
The Associated Press contributed to this report.