FRANKFURT (Reuters) - German retailer Metro AG is trying to convince investors of its value as it fights to stay in the German index of 30 leading companies, its chief financial officer told a German paper.

Metro, the world's fourth largest retailer, is currently in danger of dropping out of the Dax <.GDAXI> when the German stock market operator meets in September to review constituents of the indices.

The index rankings are based on trading volumes and the value of the shares in free float. Metro -- owned 50.01 percent by the Haniel and Schmidt-Ruthenbeck families -- has a free float of only 40 percent which has a market value of 3.2 billion euros ($3.9 billion), putting it in 36th place and in the drop zone.

Truck maker MAN is also in danger of dropping out, while car parts and tyre maker Continental is at present the most likely to move up into the DAX.

Metro shares have lost 25 percent of their value over the last year as the economic climate worsens and shoppers rein in spending. Dropping out of the Dax would pressure shares further as index-linked funds remove it from their portfolio.

"Our group market capitalization is currently 8 billion euros, but the value of our real estate alone is significantly more than that," Metro CFO Mark Frese said in an interview with Boersen-Zeitung.

Frese said the group had to try to communicate to investors that measures to reduce costs and improve its prices to get customers in its stores were taking effect, as shown with its second quarter results in July.

"But even if we don't stay in the Dax, then we will still be the world's fourth largest retailer, with enormous growth potential," Frese said. ($1 = 0.8132 euros)

(Reporting by Victoria Bryan; editing by Ron Askew)