MOSCOW (Reuters) - Russian economists warned the government on Thursday a new law that might force their research centers to register as "foreign agents" could have a disastrous impact on the economy.

In a letter published by business daily Vedomosti, 15 academics said their funding and cooperation with the government was threatened by the law, which President Vladimir Putin's opponents say is mainly intended to stifle dissent after protests.

Critics say the law will reduce the independence of non-governmental organizations that are funded from abroad and involved in what are loosely defined as "political activities".

Prosecutors have raided the Moscow offices of international advocacy groups in recent months, including Amnesty International, as well as the headquarters of vote monitor Golos and the independent Levada Center polling group.

The letter's publication following the flight abroad of liberal economist Sergei Guriev in a new sign of pressure on people or groups independent or critical of Putin.

"Continuing with the cruel and lawless application of the law on foreign agents ... will lead to the closure of analytical centers, a drop in the quality of economic analysis and expertise, and the removal of mechanisms to support and keep up standards in the profession," the economists wrote.

Putin has called for budget stimulus to get the slowing Russian economy back on track, putting him at odds with Prime Minister Dmitry Medvedev, who favors a tighter fiscal policy.

The central bank, where senior Kremlin aide Elvira Nabiullina takes over the reins next month, has also come under pressure to cut interest rates to boost growth.

The group of economists was led by Yevsey Gurvich, who heads a think tank that advises the Finance Ministry and is regarded as close to Alexei Kudrin, a liberal former finance minister who is popular with Western investors.

"There has already been a period in our history when economic science and economic analysis was fully controlled by the state. As a result ... incompetent decisions were taken on economic policy. It is well known how it turned out for the Soviet economy," they wrote.

The economy was in a state of collapse when the Soviet Union was dissolved in 1991, contributing to its breakup.

Many groups are resisting registering as "foreign agents" under the new law because it has echoes of the Cold War.

The Kremlin denies cracking down on opponents and Putin says he wants to prevent "foreign meddling" in Russia.

(Reporting by Timothy Heritage; Editing by Douglas Busvine, John Stonestreet)