Russian lawmakers were preparing to vote Tuesday on a bill introducing fines and detention for homosexual "propaganda," a measure critics fear will be used to justify repression of gays.

The Duma lower house was expected to pass the bill which bans "propaganda of non-traditional sexual relations" to minors by Russians and foreigners as well as media organisations.

The bill's authors had earlier referred to homosexual relations but introduced the softer wording for the second as well as third and final readings expected later in the day.

Some 200 to 300 people, including Kremlin supporters and religious activists, gathered outside the Duma to express their support for the bill.

"Russia is a country of traditional values, in which more than 90 percent of the population supports the ban on propaganda of homosexuality among minors," said Sergei Zheleznyak, a lawmaker of ruling United Russia party, in a comment published on the Duma's website ahead of the reading.

"It's a preventative law. I think it should be adopted," said another United Russia lawmaker, Nikolai Bulayev, in televised remarks.

The controversial bill would make it an offence to say that gay relationships are equal to "traditional", or heterosexual, ones.

If individuals use media or Internet for such "propaganda" they can be fined up to 100,000 rubles ($3,000), while organisations can be fined up to one million rubles and can be closed down for up to 90 days.

The bill also targets foreigners, apparently because international gay rights activists such as Britain's Peter Tatchell have regularly travelled to Russia to support gay pride events.

It says that foreigners who use media or Internet for propaganda can be fined up to 100,000 rubles and can also be held in police cells for up to 15 days and be deported.

After the Duma lower house passes a bill in its third reading, it then has to be passed by the senate and is finally signed into law by President Vladimir Putin. The bill backed by United Russia is expected to become law.