* Fortescue now aiming for Sept qtr sale of TPI
* Sale of port and rail assets estimated to raise up to A$4 bln
* Fortescue seeking to cut $10 bln debt pile (Adds detail on sale plans, debt level, comment)
SYDNEY, June 20 (Reuters) - Fortescue Metals Group said the proposed sale of a stake in its rail and port assets in Australia's iron ore belt that could net around A$4 billion ($3.8 billion) was on track, but would be delayed by some months.
Australia's third-biggest iron ore miner has been scrambling to shore up its debt-laden balance sheet amid volatility in the iron ore market and as it ramps up production of the steel making raw material.
Fortescue unveiled plans in December last year to offload a minority stake in its coveted infrastructure assets which it calls The Pilbara Infrastructure, or TPI. Only two other companies, BHP Billiton and Rio Tinto, own rail lines in Western Australia's remote Pilbara region and both have refused to share them with other producers.
Fortescue had aimed to sell a stake in TPI by the end of June but said on Thursday it now expects to announce a deal, if one is reached, in the September 2013 quarter.
"The level of interest generated has necessitated a longer period of evaluation than previously contemplated," Fortescue said in an update on its operations.
Fortescue, which expects to have net debt of about $10 billion by June 30, said it was not under pressure to sell an interest in TPI.
The company has shortlisted potential investors, but hasn't named them. Sources say potential buyers include infrastructure investor Brookfield Infrastructure Partners, which already has a rail arm in Western Australia. Neither Brookfield nor Global Infrastructure Partners, which is also considered a contender, were immediately available to comment.
TPI assets include 280 km ( 175 miles) of rail lines and access to Port Hedland, the word's largest iron ore export terminal, which is also used by BHP Billiton.
A key factor reckoned by analysts to be weighing on the deal is that the company wants to sell only about 40 percent in TPI, leaving potential buyers with a lack of control over the asset.
Fortescue is also under pressure from junior rivals such as Brockman Mining Ltd to cede access to infrastructure.
News of a delay in clinching a deal before the end of the financial year weighed on Fortescue stock, which was already down in step with other miners on global growth concerns. Fortescue shares were last down 6.6 percent at A$3.14 in an overall market down about 2.5 percent.
($1 = 1.0486 Australian dollars) (Reporting by James Regan and Jackie Range; Editing by Richard Pullin)