* Agag seeking to take control of Formula E
* Shareholders include Liberty Global
* Mercedes set to join in 2019
* Ferrari remain unconvinced (Adds detail, Mercedes and Ferrari quotes)
By Alan Baldwin
LONDON, May 4 (Reuters) - Formula E founder and chief executive Alejandro Agag has made a 600 million euro ($716.34 million) bid to take full ownership of the company, the all-electric series said on Friday.
A Formula E spokesman confirmed the Spanish entrepreneur had written to the chairman of the board of directors setting out his plans.
"I strongly believe in the future of Formula E and this offer is an expression of that confidence," Agag wrote in the letter.
"For this reason I would like to make a proposal to buy all the shares in the company at a value of 600 million euros equity value."
Formula E's shareholders include John Malone's Liberty Global and Discovery Communications.
Agag told Reuters last year, when Formula E posted an operating loss of 33.7 million euros to end-July 2016, that the series would have broken even without a decision to invest significantly in marketing and promotion.
Excerpts from his letter were published by the motorsport.com website, whose owner the Motorsport Network last year acquired an undefined stake in Formula E.
Formula E also announced last month that 2016 Formula One champion Nico Rosberg had become a shareholder, without giving any details.
The city-based series held its inaugural race in 2014 and, now in its fourth season, is attracting increasing manufacturer interest with Porsche and Mercedes due to enter in the 2019-20 championship.
Full works teams include Audi, Citroen's DS and Jaguar while Nissan is due to replace Renault in 2018-19 when a new Gen2 car is introduced and BMW also becomes an official manufacturer entry.
"Formula E is an exciting platform and against all odds Alejandro and his team have managed to build a series which is interesting for many people," Mercedes F1 boss Toto Wolff said in February.
"It clearly hits the Zeitgeist, corporate boardrooms are talking about it and what he and his team has been doing is truly amazing."
The series, with audiences and costs that are far lower than Liberty Media-owned Formula One, has yet to convince the likes of Ferrari however.
"With all due respect to Formula E, I think we have a long, long way to go before that becomes a potential substitute for Formula One," Ferrari chief executive and chairman Sergio Marchionne told analysts on Thursday.
"I understand it directionally. I just don't think we're there. I think it's lacking a lot of things... I don't think in its present form it is a threat to Formula One."
$1 = 0.8376 euros Reporting by Alan Baldwin, editing by Christian Radnedge