MADRID, Sept 29 (Reuters) - Australia's IFM Investors is sticking with plans to buy a stake in Spain's Naturgy despite Madrid's move to tax windfall profits at utilities, and believes the new policy will make its offer more appealing to investors.

IFM Vice-President Jaime Siles, who is leading the bid, said the Spanish government's move gave an incentive for minority shareholders to take up its offer before the Oct. 8 deadline as, without the bid, Naturgy's shares might be trading lower.

Seeking to rein in soaring energy bills, Madrid passed measures this month to redirect billions of euros in extraordinary profits from the energy industry to consumers, hitting the shares of utilities such as Endesa and Iberdrola.

Naturgy has warned its shares could be hit too, while IFM says the stock is being propped up by its bid and would likely plunge after the deal closes.

"The government's regulatory change makes the offer much more attractive," Siles told reporters in a meeting in Madrid. "If it was very attractive, now I consider it unrejectable."

IFM has launched a 4.9 billion euros ($5.8 billion) bid to acquire a 22.69% stake in the Spanish energy group but the three main shareholders that hold a combined 67% of Naturgy will not tender their shares.

Naturgy's adviser Citi looked for a counter-bidder and found no one willing to pay more than IFM, said Siles, citing a report made by the energy group's board that found the offer "reasonable".

"No one in the market has been able to pay more than what IFM is offering", added Siles. "The feeling today is quite positive".

IFM has until Friday to change the price or percentage it proposed to buy and can decide before Tuesday to extend the deadline. Siles has so far ruled out changing any of these conditions for now.

IFM said it would accept a dividend cut after becoming a Naturgy investor to support the company's development plans. (Reporting by Corina Pons and Isla Binnie Editing by Nathan Allen and Mark Potter)