The Boeing Co. announced Monday it will build an extended-range version of its largest 737 model, which an analyst said should help the company regain a market niche it lost when it canceled the 757.

The new 737-900ER will fly farther and carry more passengers than the same-sized 737-900, said Mike Delaney, the chief engineer for the Renton-based 737 program.

Boeing launched the program with a 30-jet order from Lion Air, an Indonesian low-cost carrier. The airline had previously announced that it planned to buy up to 60 737s. On Monday, it finalized that deal by ordering 30 of the new 900ERs, and taking options on 30 more.

The deal is worth about $3.9 billion at list prices; however, airlines typically negotiate discounts. Boeing will start assembling the first planes next spring, and after a flight-testing program, it will deliver the first plane in early 2007.

The new plane will have exit doors toward the rear of the plane, which means airlines can put more passengers on board and still meet emergency exit requirements imposed by regulatory agencies.

With the new doors, airlines can fit a maximum of 215 seats into the 737-900ER, an increase of 26 over the 737-900.

The 900ER also will have an extra 26 inches of interior space in the back because of a reworked pressure bulkhead, and it will be able to carry additional fuel, which will stretch its range to 3,685 miles with auxiliary tanks, or about 3,250 miles without them.

That’s long enough to allow airlines to fly across continents, and that’s farther than Airbus’ competing A321, Delaney said.

Airlines will have the option of ordering the 900ER with the rear exits covered over, or “de-activated.” Delaney said that version of the plane will appeal to traditional air carriers, operating planes with first- and second-class sections, because cabin layouts are better without the rear door.

But charter carriers and low-cost airlines will likely opt for rear doors, because they’ll be able to put more seats in. “It’s a great opportunity for more revenue,” Delaney said.

Teal Group analyst Richard Aboulafia said the 737-900ER will allow Boeing to better compete against the 215-seat A321. “For a while, Boeing seemed to surrender that part of the market.

“It’ll have superb economics,” Aboulafia said. And with 215 seats, “it goes a long way toward replacing the 757.”

Delaney acknowledged as much. “We’re clearly extending the 737 family up into the range that was covered by some of the 757s,” he said.

Boeing’s now-canceled 757-200 carried between 200 and 230 passengers.