(Releads, adds analyst quote, background on economy)

By Robin Pomeroy

TEHRAN, Sept 16 (Reuters) - Iran has delayed phasing outgasoline subsidies in what analysts say may be a sign ofPresident Mahmoud Ahmadinejad's anxiety to avoid igniting apopular backlash.

Touted as "the biggest economic plan in the past 50 years",the gradual elimination of the $100 billion the state pays tokeep down the price of essential goods, had been due to start inthe second half of the Iranian year, which begins next Friday.

But a senior official said petrol pump prices would continueto be kept low by massive state subsidies for at least anothermonth.

With the economy subject to what one senior politiciancalled the toughest sanctions Iran has ever experienced,analysts say the government may be getting cold feet about theradical plan, which will inevitably push up consumer prices.

Ahmadinejad hopes eventually to divert some of the money thestate spends to keep down the price of food and fuel into directpayments for poorer families.

"People's lives will improve from the very beginning,"Ahmadinejad has said, dismissing as scaremongering the notionthat removing subsidies on vital goods will cause strife.

But the risks are great. People rioted when the governmentstarted rationing subsidised petrol in 2007 and some analystshave said big price hikes could reignite unrest which flaredafter Ahmadinejad's disputed re-election last year.

After the June 2009 vote, Ahmadinejad faced down the worststreet unrest since the 1979 Islamic revolution. The governmentsaid the ballot was fair and accused foreign powers of stoking"sedition".

PSYCHOLOGICAL IMPACT

The subsidy phase-out -- already delayed for six months dueto disagreements between Ahmadinejad and parliament -- was dueto start on Sept. 23, but a senior official said that deadlinewould be missed by at least a month.

"The (gasoline) ration will not change for this month,"Mohammad Royanian, head of Iran's Transportation and FuelManagement Office, was quoted as saying by Donya-ye Eqtesadnewspaper on Thursday. No reason was given.

"The exact and definite date will only be announced by thepresident. From now on, gasoline rationing will be announcedmonthly," Royanian said.

The government has been vague about the timing and severityof price rises and about the hardship payments aimed to help thepoor afford essentials like petrol, cooking gas and electricity.

Economists have warned of a psychological impact oninflation as consumers anticipate future price rises.

"This ambiguity about the different aspects of this lawmeans the market and families do not know how to adjust their(spending) behaviour for the coming months," Mardomsalari dailysaid in an editorial, urging the government to get on with thereforms quickly in order to clear the uncertainty.

Gasoline is particularly sensitive because tougher sanctionsover Iran's nuclear programme imposed in recent months haverestricted fuel imports. Increasing pump prices is aimed atcooling demand as well as saving state cash.

Iran announced on Sept. 7 it had achieved a massive increasein its refining capacity and no longer needed to import 20million litres of its 64-million-litre daily consumption,something traders said they doubted was possible.

Under the rationing scheme introduced in 2007, a motoristcan buy 60 litres of subsidised fuel per month for just 1,000rials per litre (around $0.11). Beyond that amount they have topay a "semi-subsidised" price of 4,000 rials.

Scott Lucas, a specialist in U.S.-Iran relations atBritain's Birmingham University, said: "The fact is thatgasoline is one of those visible areas. If price rises lead todemonstrations, it's usually over gas or food."

The official inflation rate has been steadily falling in therun-up to the subsidy phase-out, hitting a 25-year low of 8.8percent a year in August, but a senior cleric recently voicedmany Iranians' concern about the veracity of the statistics.

"Constantly, figures are presented about the reduction ofinflation, but this contrasts with what people see with theirown eyes," Grand Ayatollah Naser Makarem Shirazi said. (Additional reporting by Ramin Mostafavi, editing by PaulTaylor)