PORTLAND — The number of planes flying in and out of Portland International Jetport is on the rise even as airlines are cutting back on their over-all flights around the country.

Monthly passenger traffic at the airport topped 200,000 for the first time in August, which was up 8.7 percent from a year earlier and the 16th consecutive record-breaking month for the facility, airport officials said.

The upward trend should continue in the fall, according to a report by Joel Antolini, consultant with Seabury Airline Planning Group. In November, the passenger seat capacity of planes flying in and out of Portland is projected to increase 15 percent from November 2007, while capacity nationwide is expected to go down 9 percent in the same period.

Much of the growth in Portland stems from the emergence of low-cost carriers, which account for 28 percent of the passenger seats. JetBlue arrived in Portland in May 2006 and Air-Tran Airways in June 2007.

“They’ve grabbed that without robbing from the legacy carriers. They’ve expanded the total pie” for Portland, said Paul Bradbury, the airport manager.

Besides giving travelers more choices, the low-cost carriers have also driven down fares. The average ticket price out of Portland is down 14 percent since those carriers arrived in Maine, according to Antolini’s report.

Bradbury said passenger counts are expected to continue rising in the years ahead before plateauing in 2013. The airport served more than 1.6 passengers last year, and the number is expected to grow to between 2 million and 2.2 million in the next five years.

Meanwhile, the Manchester-Boston Regional Airport in Manchester, N.H., has had flight cuts.

Southwest Airlines, another low-cost carrier, last month announced the elimination of almost 200 flights nationwide, including three out of Manchester. Passenger volume in July was down 6 percent from a year ago, said Tom Malafronte, assistant director of air service development and marketing.

“We’ve probably lost some to the Portland area, as a result of them having two low-cost carriers,” he said.