Boeing will increase its workforce at its 737 plant in Renton next year in order to continue ramping up the production of its most popular airplane, said a company spokeswoman.

Boeing has gone on a building spree for its Next-Generation 737, with already-announced plans to increase the production rate from 31.5 planes a month to 35 planes in early 2012.

Today (Thursday) Boeing announced that it would increase production yet again to meet worldwide demand, to 38 planes a month in the second quarter of 2013.

“Increasing production is in response to customer demand for this airplane,” said Boeing Commercial Airplanes President and CEO Jim Albaugh in a company press release. “Airlines want this innovative airplane sooner to renew their fleets to serve their customers. We made this decision after careful evaluation by Boeing and our supplier partners.”

The current 31.5 planes a month is already the highest production rate ever for the 737.

Boeing spokeswoman Vicky Ray didn’t have an exact figure on how many new employees the company would hire, but it’s likely several hundred.

But the hiring and training has to start in time to produce 35 planes a month in early 2012, she said.

Boeing has about 9,000 employees in Renton, including at the 737 plant and at its Longacres Park, where the commercial division is headquartered.

A key Renton administrator has already said that further increases in Boeing production would be good news for the city.

In a statement, Tom Wrolewski, president of District 751, International Association of Machinists, said producing 38 planes a month is “a great challenge, but one our members will achieve.”

“The fact that Boeing is able to build jets at this all-time record rate is a testament to the skills and experience of the workforce here in Puget Sound,” he added. “They are an asset Boeing can’t replicate anywhere else.”

He called Boeing’s plan to hire additional workers “welcome news, both for us and for the community. The sooner Boeing brings the new people on board, the sooner our members can start training them to ensure we have a skilled aerospace workforce long into the future.”

Earlier, there was discussion Boeing would increase production to 40 737s a month, but that was just one of the options under consideration.

“We could still go higher later, but that is not a near-term decision,” Ray said.

Right now, there is a backlog of about 2,000 orders for the Next-Generation 737. So far, 5,442 versions of the current 737 model have been ordered, with 3,378 delivered, said Ray.

This year alone, 90 percent of the 278 Boeing orders are for 737s, or 250 of the single-aisle airplanes, she said.

“When you talk about the strength of the program, that would be a proof point,” she said, of Boeing’s most popular airplane.

The 2010 Current Market Outlook, Boeing’s long-term forecast of air traffic volumes and commercial airplane demand, projects a market of more than 21,000 single-aisle airplanes over the next 20 years, accounting for an anticipated 69 percent of the airplanes delivered and an estimated 47 percent of the $3.6 trillion total market value.