President Vladimir V. Putin of Russia intensified his crackdown on L.G.B.T.Q. people on Monday, when he signed new legislation that widely bans public expression of their identity in the country.

The new law makes it illegal to spread “propaganda” about “nontraditional sexual relations”  in the media, advertising, movies or on social media. It had passed the Duma, Russia’s Parliament, by a vote of 397 to 0 on Nov. 24.

Demonstrations of “nontraditional relationships or preferences” will also be completely barred from advertising, and from any outlet visible to minors.Distributing to minors any information “that causes children to want to change their sex” was also prohibited.

The law is likely to put another strain on a community that has already been largely stigmatized in a country where officials have cast the repression of L.G.B.T.Q. expression as part of a wider struggle to protect Russia from Western interference.

Mr. Putin has long cast L.G.B.T.Q. life as a Western intrusion into Russia’s traditional society and values, and proponents of the new law recently likened the fight against L.G.B.T.Q. expression to Russia’s military actions in Ukraine, which they see as a broader civilization clash between them and the West.

“We have our own way of development, we do not need European imposition of nontraditional relations,” Nina Ostanina, chairwoman of the committee on family, women and children, said during parliamentary hearings on the legislation.

Russia has banned “propaganda of nontraditional sexual relations” among minors since 2013, with steep fines or suspension of business activities for Russians, and expulsion from the country for foreigners who were found guilty. The new law extends the ban on such propaganda to all adults.

Since 2013, just over 100 cases ended up in court, according to an analysis by a Russian lawyer, Maksim Olenichev, but experts said its biggest impact was casting the community as inappropriate, making it more invisible and subject to abuses. The new law is likely to push the L.G.B.T.Q. community further underground, its opponents said.

The new law also contains a ban on propaganda for pedophilia, and a leading independent news site, Meduza, said the combination “looks like an attempt to put homosexuality and pedophilia in the same row.”

“The ban on ‘L.G.B.T. propaganda’ is a big problem,” Alena Popova, a human-rights activist, told the group Coming Out. “Now this vulnerable group is in an even more vulnerable position.”

It is unclear what the word “propaganda” means in the context of the law, but the 2013 law said it took the form of “dissemination of information aimed at the formation of nontraditional sexual attitudes among minors.” Imposition of information about these relationships “that arouses interest in such relations” also amounted to propaganda, the law said, as did spreading the “distorted idea of ​​the social equivalence of traditional and nontraditional sexual relations.”

Fines for “propaganda” of nontraditional sexual relations or preferences can rise to about $6,400 for citizens and $80,000 for organizations.

Roskomnadzor, Russia’s powerful internet regulator, will monitor the internet to identify information and programs that are affected by the ban on L.G.B.T.Q. “propaganda” and pedophilia, according to the Russian state-run news agency Tass.

The law also forbids the issuance of a rental or streaming certificate for films with materials that promote nontraditional sexual relations and preferences.

Even before the legislation was signed, Russians in the L.G.B.T. Q. community feared that it might make it harder for them to continue living in a country that is muting the expression of political and social views and personal identities of which the Kremlin disapproves.