* Qube approach narrowly beats Brookfield's formal takeover offer
* Competition regulator has concerns about Brookfield bid
* Regulator to rule on Brookfield bid Dec. 17
* Qube run by former head of Asciano's ports operations (Adds share reaction, regulator's stance)
By Byron Kaye
SYDNEY, Nov 16 (Reuters) - Australian rail and ports giant Asciano Ltd said it will allow Qube Holdings Ltd to conduct due diligence after it made an informal $6.3 billion takeover offer just above a rival bid from Brookfield Asset Management Inc.
Asciano, which has already recommended the formal offer from Canada's Brookfield to shareholders, said it would open its books to Qube and its partners as it was committed to maximising value for owners of its stock.
The Brookfield bid has raised concerns within the Australian Competition and Consumer Commission since Brookfield already owns some train tracks Asciano's trains run on. Granting Qube access to its books ensures Asciano has a serious buyout option regardless of the regulator's decision on Brookfield's bid, due Dec. 17.
Qube has said its bid would not raise red flags by the regulator as it is primarily interested in the ports business while other members of the consortium, Global Infrastructure Partners and the Canada Pension Plan Investment Board, would take the rail business.
A Brookfield spokesman declined to comment.
Qube, led by Chris Corrigan who ran Asciano's port unit for 16 years, last week made an informal cash and scrip approach for Asciano worth A$9.25 per share, just above Brookfield's A$9.22 offer.
The fight has already seen both Brookfield and Qube take one fifth of Asciano each.
Asciano shares were unchanged by the decision, trading down 1 percent in line with the broader share market. Qube shares were steady.
The battle for Asciano underscores the attraction of Australian companies in a year in which the local currency has skidded 13 percent and the share market has fallen 7 percent, cutting valuations of firms seen as well regulated and having growth potential.
Reporting by Byron Kaye; Editing by Edwina Gibbs