MOSCOW, July 12 (Reuters) - Moscow's plan to implement a new law enabling authorities to seize the assets of Western firms leaving the country failed to get through parliament before the summer recess, giving companies more time to negotiate exits.

Russia's parliamentary session ended last week without the bill being passed. That makes any progress unlikely until at least mid-September, when the lower house of parliament, or Duma, begins reviewing proposed laws in its autumn session.

Some experts now doubt whether the proposed law will be implemented at all.

"The fact that it only passed the first reading and got stuck means there is no consensus in the government about its further fate," said Tatiana Stanovaya, founder of political analysis firm R.Politik.

The delay may ease concerns that Moscow is taking a more aggressive approach to remaining Western firms, heightened by President Vladimir Putin's decision last month to seize full control of the Sakhalin-2 gas and oil project by decree.