By Francesco Canepa and Balazs Koranyi

FRANKFURT (Reuters) -European lawmakers backed on Wednesday Claudia Buch's appointment as the European Central Bank's top supervisor after a tough hearing, with some raising objections about the legality of her nomination and her qualifications.

The vote clears the way for Buch, who has been the vice-president of Germany's central bank for 10 years, to take over from Andrea Enria as the next chair of the ECB's Single Supervisory Board, which oversees the euro zone's 109 biggest banks.

But the result of the secret ballot by the European Parliament's Committee on Economic and Monetary Affairs was close, with 29 votes in favour of Buch's appointment, 23 against, and 2 abstentions.

Buch was chosen by the European Central Bank last week over Spain's Margarita Delgado, who was the European Parliament's preferred candidate because of her superior experience as a supervisor.

Most European lawmakers who spoke at the Committee's hearing criticised the ECB for disregarding their informal opinion.

Jonás Fernández, a Socialist from Spain, said Buch's nomination may have even broken a rule barring the ECB from picking a candidate from within its own Governing Council, where Buch is an alternate member to Bundesbank President Joachim Nagel.

The ECB has responded in a legal opinion seen by Reuters, arguing Buch, as an alternate, was not a Governing Council member so that rule did not apply to her.

At the hearing, Buch said she would immediately resign from her role as an alternate if appointed as chief supervisor.

ECB President Christine Lagarde said last week that the 26-member Governing Council followed the rules in Buch's selection.

LIMITED EXPERIENCE?

Marco Zanni, of the right-wing Identity and Democracy Group, asked Buch how she planned to address what he called her limited experience as bank supervisor compared with the other candidate.

Buch, 57, recalled her decade as the Bundesbank's board member in charge of financial stability, when she worked closely with bank supervisors and navigated "many difficult situations".

"I am fully confident in my ability and strengths for this position," the former economics professor added.

Responding to another question, Buch said creating a common EU insurance on deposits was crucial, breaking with Germany's long-held scepticism about an initiative that would see financial resources pooled to protect depositors across the bloc.

She added, however, that "national specificities" that work well should be kept, a likely reference to Germany's own system involving a public and private safety net for depositors.

She also pledged to simplify the annual checks that lenders undergo by cutting routine tasks.

The EU Parliament's will take a final vote on Buch's appointment in a plenary session later this year but Wednesday's backing by the committee suggests further steps in the process will be a formality.

(Additional Reporting by Frank Siebelt; Editing by Hugh Lawson, Alexandra Hudson and Tomasz Janowski)