By Noele Illien and John Revill

BERN A Swiss parliamentary investigation into the role played by state institutions in the collapse and emergency rescue of Switzerland's second biggest lender Credit Suisse will take 12 to 14 months to complete, its president said on Thursday.

The investigation committee is Swiss lawmakers' most powerful tool and this is only the fifth time such a parliamentary probe has been launched.

"The main task of the commission will be to investigate the legality, expediency and effectiveness of the conduct of business by the competent authorities and bodies in the context of the Credit Suisse crisis and to report to the Swiss parliament," the committee said in a statement.

After an initial meeting on June 16, the committee held its first regular meeting in Bern on Thursday, where it set out some of its rules.

It decided to operate under a duty of strict confidentiality for committee members and people called for questioning, citing the secrecy of documents and information to be disclosed.

The investigation, which is being led by 14 lawmakers from the country's upper and lower houses, will examine how the Swiss government and the finance ministry, acted in the run up to the crash.

It will also examine the role played by financial regulator FINMA as well as the Swiss National Bank.

Commission president Isabelle Chassot, a lawmaker from Die Mitte party, told a briefing in Bern she expected the commission to last 12 to 14 months.

UBS agreed to buy Credit Suisse for 3 billion Swiss francs ($3.48 billion) in March after panicked customers withdrew cash from their accounts at the stricken lender.

($1 = 0.8627 Swiss francs)

(Reporting by Noele Illien in Bern and John Revill in Zurich; editing by David Evans, Alexandra Hudson)