* Elliott holds 6.8 pct stake -regulatory filing
* Position taken day after SNC Lavalin agreed to buy WS Atkins
* Elliott declines to comment on move (Adds SNC declines to comment )
By Vikram Subhedar and Simon Jessop
LONDON, April 24 (Reuters) - U.S. activist investor Elliott Capital Advisors disclosed on Monday it has taken a 6.8 percent stake in WS Atkins after the British engineering and construction consultancy firm agreed to be bought in a C$3.6 billion ($2.7 billion) deal.
Elliott said in a regulatory filing that it acquired the stake in a contracts-for-difference deal on April 21, the day after Atkins agreed to be acquired by Canadian construction and engineering group SNC Lavalin.
Shares in Atkins closed on Monday at 2,100 pence, above SNC's offer price of 2,080 pence a share.
After SNC made an indicative offer for Atkins on April 3, Liberum analyst Joe Brent said in a note that the move could spark a bidding war, given growing consolidation in the industry. He declined to comment on Monday.
The stake in Atkins opens up another front in Europe for Elliott, as it presses Dutch-based paintmaker Akzo Nobel to open takeover talks with U.S. suitor PPG Industries , and separately campaigns for a restructuring at Anglo-Australian miner BHP Billiton .
Elliott's stake in Atkins makes it the second-biggest shareholder, Thomson Reuters data showed, just behind asset manager Columbia Threadneedle.
A spokeswoman for Elliott declined to comment on why the firm had taken a stake in Atkins. Spokesmen for Atkins and for SNC also declined to comment. ($1 = 1.3482 Canadian dollars) (Additional reporting by Justin Varghese and Esha Vaish in Bangalore and Allison Lampert in Montreal; Editing by Greg Mahlich)