BETHESDA, Md. (AP) It could take investigators weeks to determine what caused a massive water main to burst, sending a wave of water onto a suburban Washington road, officials said.

Workers making repairs might get clues to what triggered Dec. 23’s deluge that trapped nine motorists in the raging waters, but a forensic investigation will take weeks, said Teresa Daniell, the Washington Suburban Sanitary Commission’s interim general manager. The motorists had to be rescued by emergency workers in helicopters and boats.

The 5.5-ft. pipe that broke was installed in 1964. The flood washed away much of the earth around a nearby high-pressure gas main, leaving it with little support.

Commission spokesman Jim Neustadt said Dec. 24 that turning off the water flow to the pipe was proving harder than expected. Officials thought the repair work would take several days.

Once that is secure, crews can pump water out of the crater around the spot where the water main broke and begin repairs, commission spokeswoman Lyn Riggins said.

During a visit to the site Dec. 24, Gov. Martin O’Malley got a look at the crater left in the embankment beside River Road and the debris carried down the hill. O’Malley praised the rescue workers.

The incident underscores the importance of maintaining infrastructure built by previous generations, O’Malley said.

“It’s an easier task for us as a people to make an investment in something we can see,’’ O’Malley said. Utilities buried underground are often forgotten. “We don’t think about it if it’s working properly.’’

The state has already begun working with House Speaker Nancy Pelosi’s office to identify projects ready for construction and water projects are on the list, O’Malley said.

A backlog of projects has built up over the past 20 years, but O’Malley expects the incoming Obama administration to get the federal government “back in the game’’ with its economic stimulus efforts focused on infrastructure projects nationwide.

Montgomery County Executive Ike Leggett said he and others have been engaged in an ongoing discussion on increasing rates to pay for infrastructure maintenance, but these aren’t as interesting projects as building a community center. The public does not understand — and the public officials aren’t motivated — to focus on such issues, he said.

Officials have been talking for a long time about raising rates and no one wants to do that during hard economic times, but the work is important, said Montgomery County Councilwoman Nancy Floreen, a member of the council committee that handles such matters.

An incident like the one on Dec. 23 highlights needed spending to keep infrastructure sound.

“When you fail, you fail big time,’’ Floreen said. “When you win, nobody notices.’’

There have been several major water main breaks this year in the wealthy suburb of Montgomery County. In June, a rupture closed more than 800 restaurants and left tens of thousands of people scrambling for clean drinking water.

An investigation of the June break found that wire inside a 4-ft. wide concrete pipe was weaker than designed and corroded by acidic groundwater, according to a report to the commission.

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