WASHINGTON (AFP) - The top US air safety administrator said on Wednesday it was still far from allowing Boeing's 787 Dreamliner to fly again with a proposed fix for its faulty batteries.

"What Boeing has presented to us is a proposal that identifies a handful of probable causes that are all in the battery itself," Federal Aviation Administration chief Michael Huerta told lawmakers.

"Once we approve the plan, we have to go though the process of actually implementing the plan, which will involve a great deal of testing, a great deal of further analysis and re-engineering before these planes are back in the air." Mr Huerta said he expected to have an FAA report next week on Boeing's proposal.

All 50 of the world's 787s were grounded on Jan 16 after the lithium-ion batteries on Boeing's new cutting-edge plane overheated, causing a fire on an aircraft parked in Boston and inflight smoke on another that forced an emergency landing in Japan.

The eight-cell battery was manufactured by GS Yuasa of Japan, which was hired for the project by Thales, a French subcontractor for the all-new plane built largely with lightweight composite materials.

The lithium-ion batteries are significantly more powerful and lighter than the nickel-cadmium batteries used in other planes.

Mr Huerta said that Boeing had presented a "comprehensive" plan that offers three levels of fixes, including design and re-engineering, to make sure that fire and smoke do not reoccur.

Boeing's plan focuses on a problem on a single cell, a problem that migrates to another cell and a problem that affects the entire battery, thus affecting the aircraft.

"We're working on the cell level, the battery level and the plane level," Mr Huerta told the House Aviation Subcommittee.

The FAA gave Boeing approval earlier this month for two 787 test flights so the aerospace giant could collect data on the battery problems.

The Wall Street Journal reported this week that US government regulators have been working to give Boeing approval for test flights of its proposed battery fixes as early as next week, citing people familiar with the situation.

Boeing had told some airline customers that if testing were conducted in early March, the jets could be carrying passengers by the end of the month, according to the Journal.

But Mr Huerta disputed the report, saying: "I don't have an application in front of me for any other test flight."