President Vladimir Putin on Saturday signed the bill ratifying Russia's entry to the World Trade Organization after 18 years of often acrimonious negotiations, the Kremlin press office said.

Economists have long argued that Russia needed to join the WTO as it was the only major economy outside the body -- following China's membership in 2001 -- and the government hopes accession will stimulate growth.

The measure making Russia the 156th WTO member will become law within 30 days, after the lower house of parliament, the State Duma, approved it on July 10 and the upper house, the Federation Council, on Wednesday.

But the membership has also been controversial, with some medium-sized firms expressing concern they will be put out of business by being unable to compete against imports made cheaper by a reduction in customs tariffs.

The reduction of the tariffs was a key condition for Russia entering the WTO and they will fall from a current average level of 9.5 percent to 7.4 percent in 2013, 6.9 percent in 2014 and 6.0 percent in 2015.

According to the World Bank, WTO entry will bring a boost worth 3.3 percent of Russian GDP -- or $49 billion -- in the first three years after joining. Over 10 years, the gain will be worth 11 percent of GDP, it says.

But Senator Sergei Lisovsky warned this week that Russia was wholly unprepared to compete without trade protection against other world economies which were more used to competition and were considerably less corrupt.

Russia's journey to joining the WTO started back in 1993 but was marked by frequent rows with Western partners, objections by its foes and not least a sometimes lukewarm attitude on the part of the Russian leadership.

But Putin is now openly championing modernisation of the economy to wean the country off dependence on oil and gas exports and officials have warned progress is not possible without WTO membership.