A small dark cloud building against the inevitability of Ronald Reagan's nomination can be traced to independent-minded Florida republicans such as Walter Bell, a semi-retired businessman from this pleasant little East Coast town.

Bell, a member of the Stuart central committee, is among the 20 percent of delegates appointed to the Nov. 17 Republican state preferential convention and assumed to be overwhelmingly pro-Reagan. Bell is listed for Reagan by Florida head-counters working for John B. Connally, George Bush and Reagan (although Reagan's count cautiously calls him "leaning Reagan").

There is one dissenter: Walter Bell. "Honesty, I'm totally undecided," he told us. In poor health lately, Bell explained he had not heard any candidate offer a Republican alternative to Teddy Kennedy's health plan that appeals to people less well-fixed financially than Bell. Furthermore, Reagan's age troubles him: "We need a president who can serve eight years."

Bell attended a coffee here to meet Connally's wife, Nellie, and shows up for any Republican candidate who comes near Stuart. Like hundreds of other delegates, he will arrive early in Orlando for the preferential convention to question Connally. Bush and other candidates before making up his mind in Saturday's secret balloting. But he won't be able to question Ronald Reagan, who will get there to late to be interrogated by delegates.

Because of the Walter Bells, Florida's preferential convention is becoming a no-win situation for Reagan. At best, balloting will bring an expected win but not by an impressive margin. At worst, it could conceivably bring an upset victory by Connally that would rattle Reagon's national aura of inevitability.

Whatever the outcome in Oriando, Florida's developments have exposed defects in campaign manager John Sears' smoothly stitched strategy off lying low until Reagan's Nov. 13 announcement of candidacy. Absence and silence have not made the Florida heart grow fonder or silenced nagging doubts here about Reagan's age -- a situation worsened by a messy shakeup of his Florida campaign.

That 1,357 Florida Republicans will assemble in Orlando for a "straw ballot" unrelated to national convention delegates is testimony to the madcap nature of presidential politics today. Supporters of Rep. Philip Crane orgininally conceived the preferential convention to boost his anemic national ratings before next year's primaries.

When Crane's early promise failed, Florida seemed certain Reagan country.

After the caucuses in August and Septmber, which supplied 80 percent of preferential convention delegates (in addition to the 20 percent of party officials), Reagan forces claimed a 2-to-1 edge over either Connally or Crane.

That surely exaggerated his strength, claiming independent souls, such as Walter Bell, who are subject to no discipline. Some 400 delegates to Orlando say they are undecided; if only half that number are telling the truth, there is potential for surprise.

Reagan has made a single, one-day visit to Florida, on Oct. 9, compared with frantic courtship from other candidates. Besides inundating Florida with his wife and children, Connally was in the state himself Nov. 4 and 5 for questioning by delegates. Told that Connally had picked up four or five Reagan delegates, a national Reagan operative called this "a demeaning thing for a national candidate to go into somebody's living room to lobby for a straw vote."

Connally will be in Orando Friday night to answer questions from delegates. Bush, making a big push to pass Crane or even Connally, will arrive three days early. But Reagan's agents originally said he would not even at tend the convention unless permitted to speak before any other candidate. Because he accidentally drew "No. 1" in the order-of-speaking lottery, Reagan will be there -- in time to shake some hands but not to answer questions.

Reagan's absence from the state was protested by veteran political hand Pat Hillings before he was sacked as Florida campaign chief. Hillings complained that Charles Black, Reagan's national field director, was ruining the campaign by bringing in "Young Republican types." National Reagan leaders say Hillings, a former California congressman and Nixon sidekick, was bungling the campaign.

Washington lawyers paul Manaford, a veteran Nixon and Ford political aide, came to Florida two weeks before the convention to replace Hillings. But delegate coffees and cocktail parties still buzz with talk about why Reagan is so quiet on great issues. Whether this moves delegates such as Walter Bell to another candidate in Orlando poses an important early test for John Sears' strategy.