JERUSALEM, July 29 (Reuters) - A senior Israeli official denied on Sunday a newspaper report that President Barack Obama's national security adviser had briefed Israel's Prime Minister Benjamin Netanyahu on a U.S. contingency plan to attack Iran should diplomacy fail to curb its nuclear program.

The Israeli liberal Haaretz daily on Sunday quoted an unnamed U.S. official as saying the adviser, Thomas Donilon, had described the plan over dinner with Netanyahu earlier this month.

Nothing in the article is correct. Donilon did not meet the prime minister for dinner, he did not meet him one-on-one, nor did he present operational plans to attack Iran, the senior official, who declined to be named given the sensitivity of the issue, told Reuters.

Haaretz said the briefing was the most significant effort by high-level U.S. officials who had visited Israel in the past month, including Secretary of State Hillary Clinton, to try to dissuade Israel from launching its own military strike on Iran.

The report coincided with a visit to Israel by Obama's main rival in his reelection bid this November, Republican candidate Mitt Romney, who was due to meet the conservative Netanyahu on Sunday.

Haaretz said Donilon had told Netanyahu the Pentagon was planning for a possible decision to attack Iran's nuclear sites, and had shown him some of the plans.

The failure of talks between Iran and six world powers to secure a breakthrough in curbing what the West fears is a drive to develop nuclear weapons has raised international concerns that Israel, widely assumed to be the Middle East's only nuclear-armed state, may opt for a go-it-alone military strike.

Israel has warned the West it thinks it is only a matter of time before Iran's nuclear program achieves a zone of immunity in which bombs will not be able to effectively strike uranium enrichment facilities buried deep underground.

Iran says its program is solely for peaceful purposes.

On a visit to Jerusalem this month, Clinton said Israel and Washington were on the same page with respect to Iran, calling Iran's latest proposals to world power talks on the issue non starters.

Our own choice is clear, we will use all elements of American power to prevent Iran from obtaining a nuclear weapon, Clinton said.