An examination report received by the council in August found that the borough - which is constrained by a tight urban boundary - has capacity to provide 8,500 homes up to 2031, "significantly less than the objectively-assessed need of 17,800".
This leaves an unmet need of 9,300 dwellings.
Inspector Jeremy Youle’s report on the plan said the duty to co-operate had been passed and that work is underway between Luton and neighbouring authorities to assess where the unmet need could be met.
But the report acknowledged that final decisions had not yet been made on how to resolve the issue. "It is not possible to be sure that Luton’s need will be met in full or how and where this will be achieved," Youle said.
Luton Borough Council formally adopted the plan at a meeting this week. The move means that it has now become the council’s official policy guiding planning decisions for the next 14 years.
A report considered at the full council meeting said that the inspector's report "recognises that a number of emerging issues discussed at the examination hearings could not be resolved by the local plan at this time".
"Not least, there is the need to resolve cross boundary planning issues with adjacent areas to meet the unmet housing needs arising from within Luton and the wider Luton Housing Market Area".
The document said that, to tackle this, the council had committed to an early plan review, commencing "no later than the end of 2019 with a submitted plan and examination by mid-2021".
Paul Castleman, portfolio holder for planning and transport, said: "Not to have a local plan adopted would have left Luton open to speculative development and would not have delivered the jobs and homes that our communities desperately need. With this plan all development proposals which form a part of the Luton Investment Framework, the ambitious plan for major town-wide transformation, will be considered."