UPDATE 1-Antitrust agency could probe Intesa SP pact - source

* Inquiry could focus on Intesa Sanpaolo noncompliance

* Probe stems from merger that formed Intesa Sanpaolo

(Adds further details, share price)

ROME, May 11 (Reuters) - Italy's antitrust authority could open an inquiry on Thursday into a pact between Intesa Sanpaolo (ISP.MI) shareholders Assicurazioni Generali (GASI.MI) and Credit Agricole (CAGR.PA) unless the deal is changed, a source close to the issue said on Monday.

Generali, Italy's biggest insurer, and French bank Credit Agricole signed a consultation pact in April for their combined 10.89 percent stake in Intesa Sanpaolo, making them the largest single shareholding block in Italy's biggest bank by market value.

"If the consultation pact between Generali and Credit Agricole stays as it is, it's foreseeable that the antitrust (authority) could launch a noncompliance procedure against Intesa Sanpaolo," the source said, speaking on condition of anonymity.

A possible fine could reach 10 percent of Intesa Sanpaolo's revenues, or about 500 million euros ($680 million).

A probe could focus on whether the pact violates 2006 antitrust limits set down for Credit Agricole as part of the merger that created Intesa Sanpaolo, the source said.

Shares in Intesa Sanpaolo closed down 0.39 percent at 2.55 percent. The DJ Stoxx European banking sector index .SX7P was 1.11 percent lower. (Reporting by Alberto Sisto; Writing by Ian Simpson; Editing by Greg Mahlich) ($1=.7349 euros)