* Only Rosneft and Gazprom have rights for Arctic exploration
* Putin says protectionist law constrains output
By Gleb Bryanski
MOSCOW, Feb 29 (Reuters) - Russian Prime Minister Vladimir Putin, who is all but certain to become president after an election on March 4, said the country should allow non-state companies access to lucrative Arctic offshore oil and gas deposits.
"We made a decision (some time ago) that only state-controlled companies may work offshore in the Northern seas. This, to my mind, constrains production development," he told a meeting with activists in his election campaign.
"We have to work out what more should be done to increase opportunities (for other companies)," Putin added.
A relaxation of tough Russian laws on foreign investment in strategic mineral fields and offshore hydrocarbon resources - estimated at more than 100 billion tonnes of oil equivalent - has long been sought by foreign investors.
According to current law, only state-controlled Rosneft and Gazprom have exclusive rights to develop Arctic offshore deposits. Other companies, including foreign ones, are allowed to develop the fields only in partnership with state-owned enterprises.
One example of such a tie-up is the joint venture between Rosneft and ExxonMobil, that last year struck a deal to tap oil and gas fields in the Kara Sea.
Gazprom, Norway's Statoil and France's Total are working together on the Shtokman gas project in the Barents Sea, although they are struggling to get started on the development due to slow progress on tax breaks.
Russia aims to produce at least 10 million barrels per day of oil - the main driver of the commodities-dependent economy - until 2020.
Putin has said Russia will need to invest over $300 billion to maintain this level of crude production, while the Energy Ministry has warned output could fall by 20 percent without significant upstream exploration and development.
The prime minister is set to return to the Kremlin after the election with around two-thirds of the vote, according to latest opinion polls. He left the presidency in 2008 due to a constitutional law that limits an individual to two consecutive terms.