DUBAI (Reuters) - Former Iranian Foreign Minister Manouchehr Mottaki has announced he will run for president in an election in June likely to be dominated by seething conservative rivalries.

The presidential poll is a crucial test for Iran after the last one in 2009 ignited mass street protests in Tehran and other cities after Mahmoud Ahmadinejad's disputed re-election.

As Iran remains locked in a stand-off with world powers over its nuclear program, rifts between Ahmadinejad and rivals loyal to Supreme Leader Ayatollah Ali Khamenei threaten to tarnish the legitimacy of the state's theocratic ruling system.

"I will propose a plan in line with Supreme Leader's beliefs and the people's demands so that in a government with the name of the Islamic Republic, the president would be more than a sympathizer for the people and give something more than a future promise," Mottaki said on his website on Tuesday in a message to Iranians announcing his candidacy.

In a sign that Mottaki may not agree with the Supreme Leader on everything, a note on his website last month criticized "crude" suggestions set out by Iran's nuclear negotiators.

Diplomats and analysts say the defiant position of Saeed Jalili, Iran's chief negotiator, is firmly backed by Khamenei, who has the last word on nuclear and other state policies.

Jalili said two days of talks with world powers that ended in Almaty on Wednesday were a "positive step", but there was no sign of a breakthrough in the dispute. Iran denies Western accusations that it is seeking a nuclear weapons capability.

Mottaki is viewed as an ally of parliament speaker Ali Larijani, a conservative who lost to Ahmadinejad in the 2005 election and has since kept up an intense rivalry with him.

Mottaki served as foreign minister for five years until the president dismissed him in December 2010.

The struggle between president and parliament has intensified in recent weeks after Ahmadinejad publicly accused Larijani's family of using their position for financial gain.

Khamenei loyalists are scrambling to eradicate the power and influence of the more nationalist Ahmadinejad who they fear will back a candidate to pursue what they say is his plan to weaken the influence of Iran's clergy and the Supreme Leader.

Iranian media have suggested that Ahmadinejad is grooming his former chief of staff Esfandiar Rahim Mashaei, despised by conservatives as a "deviant" influence on the president, as his approved candidate, but there has been no official word.

To prevent the next president from challenging Khamenei's authority, his close advisers are looking to unite around a single hard-line candidate to minimize chances of the virulent political divisions leading to post-election chaos.

The Supreme Leader controls the Council of Guardians, which oversees elections and can bar candidates from standing.

Reformists are unlikely to be allowed to run unless they distance themselves from Mir Hossein Mousavi and Mehdi Karoubi, who lost out in the 2009 election and who have been under house arrest for more than two years for "seditious acts".

Both opposition leaders said the 2009 vote was rigged and their supporters took to the streets in huge numbers to protest, only to be crushed by security forces and religious militia.

(Reporting by Zahra Hosseinian and Marcus George; Editing by Alistair Lyon)