Islip Town leaders officially welcomed a fourth airline to Long Island MacArthur Airport's lineup Tuesday -- and executives for newcomer Allegiant Travel Co. hinted at growth to various Florida destinations.

The addition of Allegiant's twice-weekly flights to Punta Gorda, Fla., starting in mid-December was billed as the second triumph this summer for the town-run airport, which welcomed Alaska-based carrier PenAir and its inaugural Boston flight in July.

Islip officials have been courting new service and carriers to reverse a trend that saw the Ronkonkoma airport lose 46 percent of its daily flights between 2007 and 2012.

"The financial health of this airport is so important to our local economy here in Islip," said Councilwoman Trish Bergin Weichbrodt. "We're committed to continuing to work hard to restore the airport to achieve the success that we once enjoyed."

Allegiant announced service Tuesday to 10 new cities and 18 new markets, including Stewart  Airport in upstate New Windsor, said Jude Bricker, the carrier's senior vice president for planning. Bricker said Long Island's demographics -- 2 million potential travelers to Florida -- was a huge draw for the low-cost carrier that specializes in leisure bookings.

"We'll see how well we penetrate the market, and if we're successful, there are certainly plenty of very natural other destinations that would fit into MacArthur's service," Bricker said. When asked, Bricker did not rule out a nonstop flight to Las Vegas, the airline's base.

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"For the most part, it's more difficult to offer a lower fare across the country." But, he said, "we're certainly looking at it."

Bricker named Florida cities St. Petersburg, Orlando and Fort Lauderdale, and a seasonal trip to Myrtle Beach S.C., as potential future stops for Allegiant out of Islip.

Since 1999, Southwest Airlines, the airport's largest carrier, has dominated service from MacArthur to Florida. Bricker said Southwest, which flies to four Florida cities from MacArthur, doesn't usually compete with Allegiant.

"Southwest, for the most part, ignores what we do," Bricker said. "I don't think there's going to be a competitive response, but if there is, then the people of Long Island win."

Southwest spokesman Brad Hawkins called Southwest a "creature of competition."

"We vigorously and successfully compete against all kinds of airlines because we are in so many places," Hawkins said.

Robert Mann, president of Port Washington- based aviation consultancy R.W. Mann & Co., said it's a positive that MacArthur got a piece of Allegiant's expansion.

"As part of that 18-city package, it's important that MacArthur got there, but let's treat it as it is: It's not multi-time-of-day, nonstop service to multiple destinations," Mann said.

The airport plans to waive Allegiant's landing fees and discount a fuel-pumping charge for one year, provided the airline stays for two years, Commissioner Robert Schaefer said.

Michael Wittman, research assistant at the Massachusetts Institute of Technology's International Center for Air Transportation, lauded the move.

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"They aren't apologetic about coming into a market and seeing if the service works for six months," Wittman said of Allegiant. "If the service works great, they'll keep it around for a while, and if the service doesn't work, they'll pull the service immediately."