(Adds dropped UPDATE 1 in headline)
* Atlantia under siege from 5-Star over Genoa bridge collapse
* Accuses politicians of selectively leaking transport report
* Ruling 5-Star wants govt to revoke Atlantia's concession
* Has no clear plan to transfer contract to new owner
MILAN/ROME, July 1 (Reuters) - Italian infrastructure group Atlantia accused ruling 5-Star officials on Monday of selectively leaking a government report in a campaign to revoke the group's national toll-road concession.
Atlantia, which is controlled by the Benetton family, is under siege from leaders of the anti-establishment 5-Star party who blame the company for a bridge collapse that killed 43 people last year and accuse it of neglecting maintenance. The concession is worth a third of the group's core profits.
On Sunday night, a source told Reuters that 5-Star believed the government now had a legal opinion that justified the party's call for an early termination of Atlantia's concession.
The source said a transport ministry report, still unpublished, had found serious inadequacies in maintenance and management of the bridge and other parts of the network. Excerpts were also published on Monday by Italian newspapers.
Atlantia, whose shares fell 3% on the news in morning trade, said on Monday that it had not received any information on the report. Its bonds also fell, with the yield climbing to a 11-day high.
It denied it had neglected maintenance on its network, which is run by the group's toll-road unit, Autostrade per l'Italia (ASPI) and said any revocation of its motorway concession would require compensation equal to the value of the contract.
"ASPI objects to the orchestrated and partial way in which excerpts of the report have been handed to the press, before it has even been made available to the counterparty as required under the administrative procedure underway," it said.
Atlantia shares have lost nearly 7% of their value since the dispute between the group and 5-Star erupted into open warfare last week after party leader and deputy prime minister Luigi Di Maio sought to discuss the issue at a ministerial meeting.
However, 5-Star's coalition partner, the right-wing League opposed the move. Its leader, Matteo Salvini, has said no one should rush to judgment before investigations into the cause of the bridge collapse in the northern city of Genoa are completed.
The source familiar with the 5-Star party's thinking showed Reuters three pages of the report which concluded that "the grounds existed for a termination of the concession for a breach of duty by the concessionaire."
Reuters has not viewed the rest of the ministry's report.
Separately, Di Maio said in a Facebook post late on Sunday that "as far as we understand" there were serious maintenance inadequacies on the part of Autostrade and that compensation due to it in the event of early termination would not be "enormous."
The source said compensation would still be due to Atlantia, such as for investments made on the motorway network, but much less than the 24 billion euros ($27 billion) estimated by market analysts as the net present value of the concession due to expire in 2038.
The 5-Star party has not come up with a clear plan to transfer the concession to a new owner. It has suggested renationalising the network or holding a tender for a new concessionaire. ($1 = 0.8832 euros) (Editing by Mark Bendeich and Emelia Sithole-Matarise)