MILAN, Dec 13 (Reuters) - Enasarco has bought 1.97% of Banco BPM, the specialist Italian pension fund said on Tuesday, as the country's third largest bank prepares to appoint a new board and investors jostle for influence.

Banco BPM Chief Executive Giuseppe Castagna is running for reappointment in April after overseeing the successful tie-up of Banca Popolare di Milano and Banco Popolare, which merged in 2017 to create Banco BPM.

Enasarco's 101.5 million euro ($107 million) investment fuelled gains in Banco BPM shares which rose 4% at 3.29 euros each.

Enasarco, which manages the pensions of salespeople, paid 3.4 euros a share, a 7.6% premium to the stock's closing price on Monday.

"The investment is part of Enasarco's plans to develop its asset portfolio ... including through investments that support the country's real economy," the fund said in a statement.

A number of Italian investors in Banco BPM have struck a consultation pact to counter the influence of France's Credit Agricole which in April became the single biggest investor in the Italian bank, with a 9.2% stake.

The pact brings together Italian banking foundations and other pension funds such as Enpam and Inarcassa, which represent, respectively, doctors and engineers.

Investors who joined the consultation pact control in aggregate 7.84% of Banco BPM. Their holdings would top Credit Agricole's stake, if Enasarco were to sign up. Enasarco could not be reached for comment on Tuesday.

"Enasarco's move ... can be seen in terms of governance and reflects the will to create a strong base of local shareholders who could have a say in a possible M&A transaction," broker Equita said.

With 198 billion euros in assets at the end of September, or a fifth of market leader Intesa Sanpaolo's 1.02 trillion, Banco BPM has long sought a merger deal.

Having narrowly dodged a takeover offer by bigger rival UniCredit, Banco BPM is seen as a potential partner for Monte dei Paschi di Siena which the Treasury will be looking to re-privatise.

Castagna has repeatedly denied any interest for Monte dei Paschi.

Intesa Sanpaolo IMI CIB handled the transaction on behalf of Enasarco. ($1 = 0.9489 euros) (Reporting by Andrea Mandala and Valentina Za; editing by Jason Neely and Keith Weir)