* Former defence minister, others, in graft probes
* Authorities keen to show they're getting tough on problem
* But many Russians are sceptical of their motives
* Putin ally's statement looks like attempt to woo sceptics
By Gabriela Baczynska
MOSCOW, Dec 4 (Reuters) - An ally of President Vladimir Putin said on Tuesday she would table an amendment in parliament to double the maximum jail sentence for corruption to 20 years, urging fellow MPs to back a crackdown on one of Russia's most deep-seated problems.
The statement by Irina Yarovaya, head of a powerful parliamentary committee, appeared to be part of a Kremlin attempt to convince sceptical voters that Putin is serious about cracking down on financial crime.
Former Defence Minister Anatoly Serdyukov is one of a number of officials to have been fired or placed under suspicion in corruption investigations in recent weeks. But opinion polls show many Russians are sceptical about the authorities' motives and the seriousness of their anti-corruption campaign.
Yarovaya, a member of the ruling United Russia party which dominates parliament, said she would propose changes to the law to increase the punishment for embezzlement involving public or state resources.
"Responsibility for these crimes should be higher than for economic crimes. I think ... it should be raised to 20 years in prison," she told a news conference.
The current maximum sentence for such crimes was 10 years in prison, she said. It was unclear whether the kind of amendment she is proposing would pass, but given her status it seems likely it would garner considerable support.
Corruption has blighted Russia since tsarist times with many foreign investors citing it as an obstacle to putting money into the world's largest country, two decades after the collapse of the Soviet Union.
Russia is ranked 143 out of 182 countries on Transparency International's Corruption Perceptions Index, tying with Nigeria on a table where number 1 is the best rank.
NEW LAW ON DECLARATIONS
Putin is widely regarded to have failed to curb corruption since he was first elected president in 2000, despite saying he would impose a "dictatorship of the law".
In his latest attempt to show he is cracking down on graft, he signed a law on Tuesday obliging ministers to declare their spending and that of their families, but even this met with scepticism.
Kirill Kabanov, an anti-corruption activist, told Ekho Moskvy radio that the law would not cover spending abroad, making it less effective.
In other graft cases, the head of the Russian satellite network Glonass has been dismissed in a fraud investigation and a regional governor arrested over accusations that he stole funds meant for September's Asia-Pacific Economic Cooperation summit.
An opinion poll by the independent Levada research centre showed that all the recent talk of an anti-corruption campaign had failed to boost support for Putin or for Prime Minister Dmitry Medvedev.
The same survey also showed that some 40 percent of Russians thought the dismissal of Serdyukov was the start of a reshuffle of officials who have been abusing their posts. However, just as many people said they thought it was merely part of a power struggle between various interest groups around Putin.
Russia's Defence Ministry channels billions of dollars every year through the country's arms industry, the world's second-largest defence exporter. A military prosecutor said last year that one fifth of the military budget was stolen.
Putin named a loyalist, Sergei Shoigu, to head the ministry but few see corruption ending.
"This will not change the corruption schemes. This is just a bit of cleansing," said Natalia, a Moscow law student who declined to give her last name. "If it was a genuine fight with corruption, I'm afraid they would have to send all the ministers away". (Additional reporting by Steve Gutterman; Editing by Andrew Osborn)