WASHINGTON — After spending nearly $300 million on a new computer system to handle disability claims, the Social Security Administration still can’t get it to work. And officials can’t say when it will.

Six years ago, Social Security embarked on an aggressive plan to replace outdated computer systems overwhelmed by a growing flood of disability claims. But the project has been racked by delays and mismanagement, according to an internal report commissioned by the agency.

Today, the project is still in the testing phase, and the agency can’t say when it will be operational or how much it will cost.

In the meantime, people filing for disability claims face long delays at nearly every step of the process — delays that were supposed to be reduced by the new processing system.

“The program has invested $288 million over six years, delivered limited functionality, and faced schedule delays as well as increasing stakeholder concerns,” said a report by McKinsey and Co., a management consulting firm.