The search for a new chief executive officer for the Steamship Authority took an unexpected turn late yesterday when one of the leading candidates for the job suddenly dropped out.

Rear Adm. George Naccara withdrew his name yesterday, for reasons that are unknown.

A career officer in the Coast Guard who is currently the commander of the first district, Mr. Naccara was one of five finalists for the CEO spot at the boat line. He was considered by many to be among the top two candidates in the field of finalists, if not the top candidate.

"I believe that the admiral was extremely qualified and based on his experience and his interview I can say that he was a leading candidate, absolutely," said Falmouth boat line governor and board chairman Galen Robbins yesterday afternoon. Mr. Robbins had just learned that the admiral had withdrawn his name as a candidate for the top post at the SSA.

The news was communicated to the boat line and to board members yesterday afternoon by John Jay, the managing director for Executive Resources International. Mr. Jay is a professional headhunter who led the search for the new CEO at the boat line.

The boat line board completed two days of interviews with the five finalists last week.

The four remaining candidates are:

* Jean-Ives Ghazi, a ferry entrepreneur who is the vice president and regional director of Spirit Cruises in Norfolk, Va.

* Carolyn Kiley Moore, a marine consultant and former CEO and president of Bay State Cruise Co. in Boston.

* John D. O'Brien, the outgoing CEO of the Cape Cod Chamber of Commerce.

* Thaddeus Jankowski Jr., the deputy city manager for the city of Portsmouth, N.H.

SSA governors were set to discuss the candidates - and possibly vote for one - today at a special meeting in Hyannis. Yesterday Mr. Robbins said a new candidate had been introduced into the mix by Mr. Jay - he said the new candidate is an Andover attorney named Fred C. Raskin who had apparently submitted his resume to Mr. Jay this week.

Mr. Robbins said Mr. Jay described the new candidate as highly qualified. He said the candidate had coincidentally submitted his resume to Mr. Jay this week in response to an advertisement that the boat line had run in the Wall Street Journal.

At press time yesterday, Mr. Robbins said he was still in discussion with SSA general counsel Steven Sayers about whether it was appropriate to interview the new candidate at this morning's meeting.

Mr. Robbins said he and Mr. Sayers would arrive at a decision later in the evening.

"He is apparently highly qualified and I would like to interview him tomorrow, but we will only do that if Mr. Sayers agrees that it is okay," Mr. Robbins said. "I am very disappointed that the admiral dropped out, and now we have to look again at the mix of candidates that we have," he added.

Mr. Robbins said there will be no vote this morning, but he said he hopes the board can agree on narrowing the field and inviting a small number of candidates back for a second interview next week.

The SSA monthly board meeting is set for next Thursday. Mr. Robbins said the second interviews and a final vote could be accomplished on that day.

"I think that having a good process is what this is all about, and I feel very strongly that we continue to move forward with this," he said.

A formal search has been under way for a new chief executive since last August, when general manager Armand Tiberio announced his resignation. Boat line treasurer Wayne Lamson has been acting general manager since Mr. Tiberio left in September.

The board voted to upgrade the job title from general manager to chief executive officer.

The salary for the position had been reported at $109,000, but after some questioning last week, the board confirmed that the range is in fact $100,000 to $200,000.

Following the interviews last week there was general consensus - even among some of the boat line's harshest critics - that the candidates were all highly qualified and that the interview process had gone well.

"I think it was a terrific slate of candidates," said Susan Shephard, who lives in the village of Woods Hole.

"So far it's been an excellent process - and I continue to be impressed by my fellow board members, and by their good will and their integrity," said Vineyard boat line governor Kathryn A. Roessel earlier this week.

Denys Wortman of Vineyard Haven, one of a handful of Vineyard residents who sat through the entire interview process, suggested to the board last week that they do what Harry Truman would have done.

"I'd write a letter to myself about all the candidates and how they impressed me. Then I'd put the letter in a drawer and take it out tomorrow," Mr. Wortman said.