UPDATE 3-Thomson SA calls bankruptcy rumour groundless

* Says creditor talks are constructive

* Shares fell 20 percent on default rumour

* Moody's downgraded on Tuesday

* Deadline for creditor talks June 16

(Recasts, adds closing price, market value, rivals)

By Julien Ponthus

PARIS, May 20 (Reuters) - Debt-laden French multimedia firm Thomson SA (TMS.PA: Quote, Profile, Research), which brings Technicolor to cinemas and set-top boxes to households, on Wednesday called rumours of its bankruptcy groundless after its shares dropped steeply.

It said talks with banks and bondholders owed some 2.9 billion euros were "going on and are constructive."

Traders said the shares, which closed down 15 percent after plunging as much as 20 percent, were hit by rumours the company was close to bankruptcy.