(Corrects to make clear government may not sell whole stake in paragraph 2, adds byline)
* Sale of ADP stake part of privatisation drive
* Vinci already holds 8 percent of airport operator
* Government may offer its stake in early 2019
By Clara Denina and Dasha Afanasieva
LONDON, June 15 (Reuters) - Construction company Vinci has approached investors to launch a multi-billion-euro bid for part of French airport group Aeroports de Paris (ADP), the largest of President Macron's planned state sell-offs, four financial sources said.
The deal, among the first of the planned privatisations, would see France sell all or part of its stake of 50.63 percent in the group which runs Charles de Gaulle and Orly airports outside Paris and has a market cap of 19.63 billion euros ($22.78 billion).
The French government said this week it would prepare the legal ground to sell stakes in some of its corporate assets, including ADP, energy group Engie and lottery monopoly FDJ.
Two sources said Vinci, which already owns 8 percent of ADP and has publicly expressed interest in a bigger stake, has approached pension funds to become partners, including Canada Pension Plan Investment Board (CPPIB), Ontario Municipal Employees Retirement System (OMERS) and Ontario Teachers' Pension Plan (OTPP).
CPPIB and OMERS declined to comment. Vinci and OTPP did not immediately respond to requests for comment.
A third source said he expected the sale to be formally launched in the first quarter of 2019, due to the complexity of the structure.
Given the size of the asset, banking sources have speculated that the government's stake should be broken up into chunks to be sold off separately or be split into different arms.
One of the sources said he expected U.S. and Middle Eastern funds to be preparing bids, possibly forming consortiums.
European airports have been a lucrative business for private equity firms and pension and infrastructure funds over the past few years because they offer strong growth potential from increasing global travel and services such as shops, on-site hotels and car parking.
Investor Macquarie is preparing to sell Brussels airport this summer, sources familiar with the situation said.
In Britain, banking sources expect infrastructure fund Global Infrastructure Partners to sell investments in Edinburgh and Gatwick airports in the coming year or two in what could be a test of investor sentiment on the eve of Britain's exit from the European Union.
$1 = 0.8617 euros Editing by Edmund Blair