Presidential Airways, the fledgling Reston-based airline, today will announce plans to nearly double the number of cities it serves by the end of February.

The four-month-old airline expects to add flights to Montreal and to Sarasota and Daytona Beach in Florida to its current roster of 11 cities, a company spokesman said yesterday. In addition, Presidential will announce an agreement with Hyannis, Mass.-based Gull Air to expand service in Massachusetts to Martha's Vineyard, Hyannis, Nantucket and New Bedford, as well as to the Bahamas. The new routes will give Presidential a total of 19 cities served. The company will add two planes to its fleet next month as well, the spokesman said.

Although the expansion is in line with Presidential's business projections, the company concedes that it has been shifting its service focus. Originally, the airline -- founded by Harold Pereti, the former president of People Express -- intended primarily to use Dulles International Airport as a hub to link Allegheny Valley cities to cities in Florida and the Northeast.

"We're now focusing more on systemwide interchange than individual markets," said Geoffrey T. Crowley, Presidential's senior vice president of marketing. "We're leaning away from frequency of flights to markets and focusing on connections."

For example, Presidential has cut in half the number of its daily flights from Dulles to Cincinnati because of increased competition at Dulles. To help compensate, the company is becoming a bridge airline to other commuter airlines such as Gull, particularly in New England and Florida.

Presidential officials said the airline carried more than 67,000 passengers in December, representing a 41 percent increase over its November levels, its first full month of operation. At the same time, its "load factor" -- number of revenue-producing seats per mile -- increased 10 percentage points to 47.3 percent, a figure the company said is above what it had expected.

However, Crowley conceded that "Our yield isn't what we'd like it to be," citing fare wars as the reason for lower-than-desired revenue. For example, the company now charges $29 for a Dulles to Cleveland flight versus $49 two months ago.

"Their traffic has been good," said Tim Petty, an airlines analyst at L. F. Rothschild. "It's indicative of the fact that they are attracting people to Dulles, but we haven't yet seen the financials."

Petty praised the Gull arrangement as "beneficial to both parties" and said that Presidential's major concern would be managing its profitability amidst the fare cutting.