CARACAS Tue Feb 10, 2015 8:19pm EST

Venezuela launched a "free" foreign exchange platform on Tuesday that will likely devalue the bolivar in efforts to bolster state coffers amid tumbling oil revenue, although it risks causing a spike in already soaring inflation.

The change amounts to an easing of 12-year-old currency controls and marks a small step toward a market economy as the state-led model created by late socialist leader Hugo Chavez struggles with shortages, swelling grocery lines and recession.

However, the changes by President Nicolas Maduro's government do not eliminate the unwieldy three-tiered exchange structure seen by investors as the country's principal stumbling block to economic growth.

The change could lead to billions of dollars in write-downs by foreign corporations with exposure to Venezuela including General Motors Co (GM.N), household goods maker Procter & Gamble Co (PG.N) and drugmaker Merck & Co Inc (MRK.N).

The new platform, called Marginal Currency System or Simadi, is the third system in a three-tier exchange control mechanism and will allow for legal trading of foreign currency based on supply and demand, said Finance Minister Rodolfo Marco.

"This third mechanism is open, free, in which bidders and buyers exchange offers," Marco said during a press conference with Central Bank President Nelson Merentes.

The currency controls have been providing U.S. dollars at three different rates: 6.3 bolivars for food and medicine, and two complementary rates of around 12 bolivars and 52 bolivars for other goods through systems known as Sicad I and Sicad II.

But dollars fetch nearly 190 bolivars on the black market, according to widely referenced website dolartoday.com.

WHAT PRICE?

Marco and Merentes did not say what the open rate would be when the market kicks off in coming days. They predicted the new platform would help lower the parallel rate.

Brokerage sources consulted by Reuters say the rate could begin around 120 bolivars, substantially lower than on the black market but still more than double the lowest existing rate.

Local consultancy Ecoanalitica estimated a starting price of 130-140 bolivars, an average price of 115 throughout 2015, and a total offer of $7.5 billion via that system in the year.

The dollars, Econalitica said, would come from state oil company PDVSA, other oil companies operating in Venezuela, off-budget sate funds such as Fonden, and via Venezuelan bonds.

Taking into account the three different tiers, "that would make the average 2015 exchange rate 46.6 bolivars per dollar, a devaluation of 56.5 percent compared to 2014," it said.

Opposition critics slammed the announcement as an insufficient measure that will do little to address the decaying economy, which one former government minister recently described as becoming the "laughing-stock" of the region.

"If devaluation were the solution, we would be Switzerland!" wrote opposition-leaning economist Miguel Angel Santos via Twitter, noting repeated devaluations during the 16 years of rule by the late Chavez and Maduro.

PLUNGING REVENUES

The tumbling price of oil, which provides nearly all of Venezuela's hard currency, has left the 12-year-old exchange controls struggling to provide dollars to ensure steady supplies of products such as detergent and milk that are increasingly scarce around Venezuela.

Maduro, speaking late on Tuesday, said Venezuela's revenues had fallen 60 percent due to the oil price decline, and the country was ready for another two years of "low or very low" prices.

However, all social welfare projects and foreign debt commitments, starting with the 1 billion euro Global 2015 issue VE021485187= coming due on March 16, would be honored, his economic officials said.

Venezuela had the worst economic performance in Latin America last year, with 2.8 percent GDP contraction and officially-estimated 64 percent inflation.

Dismay over the state of the economy, and particularly of product shortages, has pushed Maduro's approval rating down to 22 percent, according to local pollster Datanalisis.

"Despite the fanfare that is likely to accompany the apparent shift towards a market-based foreign exchange system, we doubt that it will solve Venezuela's deep economic problems," Capital Economics said in a note on Tuesday's changes.

A further spike in inflation, due to the higher cost of imports for businesses, could spur voter indignation and leave the ruling Socialist Party unable to maintain its majority in legislative elections to be held later this year.

Both Marco and Merentes, however, denied there would be an inflationary impact. They said 70 percent of the economy's needs would be covered by dollars sold at the 6.3 rate.

The Sicad I auction system will continue to hold periodic auctions for specific sectors of the economy and will for the moment continue providing dollars at the rate of 12, Marco said, adding that rate would change over time.

The new Simadi market will replace the Sicad II system.

Investors generally interpret devaluations positively because they leave the government with more hard currency available to service debt.

Venezuelan bonds, which have been trading at distressed levels on fears of a possible default, were up across the board on Tuesday, with yields on several dropping to one-month lows.

The Global 2026 VENGLB26=RR bond was up 2.750 points in price to yield 26.841 percent while the Global 2022 VENGLB22=RR rose 3.180 points to yield 31.717 percent.

Equities investors face billions of dollars in write-downs by U.S. corporations with exposure to Venezuela, as many have been unable to repatriate bolivars back into dollars due to delays in the currency controls.

At least 40 major U.S. companies together carry at least $11 billion of bolivar assets on their books, concentrated among 10 companies that have disclosed about $7.3 billion in assets linked to the country's currency system.

Other foreign companies with notable exposure to Venezuela include Spain's Telefonica (TEF.MC) and German drugmaker Bayer (BAYGn.DE).

Some companies have already taken charges on their Venezuela exposure, including Kimberly Clark (KMB.N), Ford (F.N) and Schlumberger (SLB.N). General Motors last week said in its annual report that instability in Venezuela could lead to a $900 million hit to earnings.