* Putin tells rights council to make suggestions for amnesty
* To mark 20th anniversary of post-Soviet constitution
* Has not ruled out amnesty for 12 on trial over protest
By Steve Gutterman
MOSCOW, Sept 26 (Reuters) - Russian President Vladimir Putin is considering a prison amnesty later this year, a gesture that could enable him to counter critics who say the courts have been used to silence his political foes.
In an order posted on the Kremlin website on Sept. 24 but publicised on Thursday, Putin told his human rights council to make suggestions for an amnesty marking the 20th anniversary of Russia's adoption of its post-Soviet constitution, in December.
Putin's opponents are watching for signs of conciliatory gestures after what they say has been a clamp-down on dissent and curtailment of freedoms since he won a third term last year.
Critics say Putin has used the courts to sideline opponents, citing, for example, the jailing of former oil tycoon Mikhail Khodorkovsky and members of the punk protest band Pussy Riot.
Putin, who denies interfering with the judiciary, said last week he did not rule out an amnesty for 12 young people on trial for violence at a protest before his inauguration in May 2012.
Analysts said any amnesty was likely to be limited in scope and highly unlikely to include prominent figures such as Khodorkovsky or protest leader Alexei Navalny.
Navalny was sentenced to five years' jail for theft in July, after a trial he said was the Kremlin's revenge for his activism. His appeal is scheduled to be heard next month.
Putin's order, which gave the council until Oct. 15 to submit its proposals, gave no indication of who might fall under the amnesty, which would be enacted by parliament.
Asked whom it might cover, Putin's spokesman, Dmitry Peskov, said it was too early to tell.
A protest movement against Putin, a reaction to allegations of fraud in a December 2011 parliamentary election, lost steam after his inauguration to a new six-year term that he has hinted may not be his last.
But Navalny's strong second-place showing in Moscow's mayoral election this month underscored significant opposition to Putin and his ruling United Russia party, particularly in big cities. (Additional reporting by Thomas Grove and Alexei Anishchuk; Editing by Robin Pomeroy)