MIAMI — Park rangers discovered 20 “tar balls” on a Key West shore and spotted oil residue farther west in the Dry Tortugas today, stirring fear that the first sign of the massive BP oil spill had washed up on Florida’s shores.

The Coast Guard urged calm and sent samples of the 3- to 8-inch flattened tar balls for lab analysis in Groton, Conn., to determine whether the hazardous waste was from the massive leak in the Gulf of Mexico or perhaps oil remnants from a passing ship.

“There is no proof or reason to believe these tar balls are from the Gulf at this point,” said Anna K. Dixon, a Coast Guard Navy lieutenant, junior grade, from Key West. She said that analysis of the tar balls’ origins would not be complete before day’s end.

Still, the discovery, coupled with a grim new tracking map and a wider federal fishing ban in the Gulf of Mexico, stirred fears of a financial impact on Florida.

“While I always hope for the best, this is looking like really out-of-control bad,” Florida Democratic Sen. Bill Nelson said about fresh research by the University of South Florida College of Marine Science in St. Petersburg. A team there predicted the Deepwater Horizon’s slick would reach the Keys by this weekend – and Miami next week.

In the Keys, however, a midday survey found a second “oil residue” sighting at Loggerhead Key in the Dry Tortugas, said Larry Perez, information officer for Everglades National Park.