By Corina Pons

CARACAS (Reuters) - The slump in global oil prices has heightened pressure on President Nicolas Maduro to enact politically risky reforms to bolster Venezuela's weak public finances and its ability to pay down debt.

Crude prices under $85 have given new voice to reformers within Maduro's government, and critics outside, who say he needs to make urgent changes.

"The government continues to study the changes ... The decisions will come bit by bit," a senior official at state oil company PDVSA said, explaining a package of reforms that were mooted earlier this year and include unifying a complex system of exchange rates - effectively devaluing the bolivar currency.

A hike in domestic gasoline prices, currently the cheapest in the world at less than 2 U.S. cents per liter, is also under discussion although the official said that any policy changes would be implemented gradually to minimize public backlash.

The idea of a fuel price hike is being debated by the National Assembly and its energy commission president, Fernando Soto, said it could be decided by year end. "There's a majority consensus that we're practically giving away gasoline."

Any change to the currency control regime would, sources and economists say, probably mean weakening the lowest official rate of 6.3 to the dollar to double that or more.

Dollars are currently available at two other official rates of about 12 and 50 bolivars, while they trade at 100 on the black market.

The reforms would give Maduro's government some much-needed fiscal breathing space and help to ease concerns over whether it will be able to service its debt, although they could also fuel inflation and weaken support for his government.

Over 90 percent of the state's foreign revenues come from oil so those fears have deepened as the price of oil falls.

"If the government doesn't make adjustments, any annual (oil) price under $90 dollars will be a problem," said Benjamin Ramsey, analyst with JP Morgan.

Story continues

The bid price on Venezuela's benchmark sovereign bond due 2027 has fallen 32.5 percent to 60 cents on the dollar in the last 2-1/2 months, with the yield popped up to nearly 17 percent.

The cost for insuring a $10 million trade on Venezuela's sovereign debt for 5 years surged again on Thursday, to $4.175 million. That is almost triple the price of $1.5 million in late June.

CRUDE SHOCK

The four-month rout in oil markets, driven by signs of lower growth and demand for crude in Europe as well as signs that OPEC's core Gulf members are in no hurry to cut production, has left Brent crude at under $84 and U.S. crude below $82.

It could not have come at a worse time for Venezuela, which is already grappling with an economic slump, inflation running at above 60 percent and currency restrictions that have led to widespread shortages.

The government also faces looming payments on foreign debt and in arbitration cases following nationalizations under socialist leader Hugo Chavez, who led Venezuela from 1999 until his death from cancer last year.

And reforms aimed at improving public finances carry political and social risks.

Maduro's approval ratings have already fallen to about 35 percent, analysts expect the economy to shrink between 1 and 4 percent this year and there are important legislative elections in 2015.

Fuel price hikes are particularly sensitive in Venezuela, where hundreds were killed in riots over the issue in 1989. Since then, successive governments have been reluctant to risk new violence even though prices are extremely low.

In a sign that he was concerned about the political cost of reforms, Maduro last month removed their key proponent in his team, Rafael Ramirez, from his posts as vice-president for the economy, oil minister and head of PDVSA.

But the continued oil price slump has forced the government to again look at making changes.

ELECTION RISKS

With the economy in trouble, opposition parties could mount a strong campaign for the parliamentary elections at the end of 2015. If the ruling Socialist Party loses its legislative majority, its foes might then be encouraged to push for a recall referendum against Maduro in 2016.

"It's the first time an oil price fall is happening so close to an election cycle," local economist Richard Obuchi said. "It's only manageable if it's temporary."

Maduro needs strong government revenues to finance the political campaign and the popular social programs that underpinned Chavez's rule, and now his own.

"The government has less maneuvering room with every new day", said Diego Moya-Ocampos, a Venezuelan analyst with IHS, saying the government would face "serious difficulties" if Venezuela's oil barrel price fell under $80.

Venezuelan crudes, which normally trade at a discount to benchmark grades because they are mostly heavy and high in sulfur, have averaged $94.99 this year but the weekly price fell to its lowest in nearly four years - $82.72 - on Friday.

The PDVSA official said the company viewed the price fall as only a "cyclical phenomenon." But if they stay around current levels, Venezuela could lose about $12 billion in revenues over the next year, local think tank Sinters Financier has estimated.

That is about the same amount the government says it pays annually to subsidize local gasoline prices.

With reserves at an 11-year low of $19.8 billion - down from $29.7 billion at the start of 2013 - the government is in a squeeze, especially given it faces a roughly $10 billion annual debt bill over the next three years. Bondholders, though, say any default risk appears to be mid-term, not in coming months.

In addition to its debt load, Venezuela has to pay roughly $1 billion to Exxon Mobil over a 2007 nationalization, and could face a bigger bill next year in a similar but larger claim brought against it by ConocoPhillips.

(Writing by Alexandra Ulmer; Editing by Andrew Cawthorne and Kieran Murray)