MADRID - Infrastructure giant Ferrovial said on Friday it had reached a new agreement with French private equity fund Ardian and Saudi Arabia's Public Investment Fund (PIF) to sell the bulk of its 25% stake in Heathrow airport while keeping 5.25%.

Under the new agreement that also involves other sellers, Ardian and PIF will acquire 22.6% and 15% respectively of FGP Topco, which is the parent company of Heathrow Airport Holdings Ltd, for a total of 3.26 billion pounds ($4.13 billion).

Under an initial agreement announced last year, Ferrovial would have disposed of its entire stake for 2.37 billion pounds, valuing the whole airport at 9.48 billion pounds. The new agreement values Heathrow at 8.66 billion.

The Spanish-origin company that moved its holding to the Netherlands last year, did not disclose how much it would receive under the new agreement, which is subject to regulatory approval, or who the other selling shareholders were.

The company and other partners will retain 10%, it said.

Ferrovial that builds and manages highways and airports is focusing on its expansion in the United States, where it is building a new terminal at New York's John F. Kennedy International Airport.

The company has said it expects to complete the Heathrow sale by the end of 2024.

At the same time, Ferrovial is considering to join its partner, Australian financial group Macquarie, in a potential sale of stakes in three other British airports in Aberdeen, Glasgow and Southampton, an executive of Ferrovial said in May.

The pace of deal-making in the European airport sector is picking up, after this year Vinci Airports acquired a 50.1% stake in Edinburgh Airport.

($1 = 0.7886 pounds)

(Reporting by Corina Pons, editing by Andrei Khalip and Alistair Bell)