Competition for the lucrative Northeast business-traveler market is heating up as JetBlue Airways Corp. (JBLU) and Delta Air Lines Inc. announced this week they are both adding more flights in the region.

JetBlue announced a new service on Friday between Boston and Washington, D.C., a day after Delta said it was offering more flights on its shuttle service between the two cities and New York. JetBlue recently added service between New York and Boston.

"The No. 1 selling point of a shuttle service is frequency," said Jim Corridore, equities analyst at Standard & Poor's. But he added that JetBlue's fares could be attractive to customers.

"Delta is probably a little worried about JetBlue's plans in the market," he said.

JetBlue plans to begin the service between Boston and Washington, D.C., on January 17, 2006, with six round trips through the week and five over the weekend. Its regular fares will be between $55 and $140 each way, the company said.

Delta, which sought bankruptcy protection in September under pressure from energy costs, low-cost rivals and a high debt-load, offers a total of 62 flights a day on its shuttle service. The company also said that Comair, its connection carrier, had increased the number of daily flights between New York and Boston to 40.

JetBlue's shares were down 8 cents to $19.21 Friday on Nasdaq.