For decades, immigrants who have followed the rules and have not broken the law have had hopes of earning a green card, a document that allows them to live legally in the United States and gain a path to citizenship.

But under new guidance issued by the Trump administration, immigrants can now be denied a green card for expressing political opinions, such as participating in pro-Palestinian campus protests, posting criticism of Israel on social media and desecrating the American flag, according to internal Department of Homeland Security training materials reviewed by The New York Times.

The documents, which have not been previously reported, show how expansively the Trump administration is carrying out a directive from last August to vet green card applicants for “anti-American” and “antisemitic” views.

The administration includes criticism of Israel as a potentially disqualifying factor, with the training materials citing as an example of questionable speech a social media post that declares, “Stop Israeli Terror in Palestine” and shows the Israeli flag crossed out.

The materials were distributed last month to immigration officers at U.S. Citizenship and Immigration Services, which is part of the Department of Homeland Security and handles applications for green cards and other forms of legal status.

They reflect how U.S.C.I.S. — long considered the gateway agency for legal migration — has rapidly transformed under President Trump into another cog in his administration’s deportation machine. The agency has worked to strip naturalized Americans of their citizenship and has hired armed federal agents to investigate immigration crimes.

The administration is also granting permanent legal residency to far fewer applicants. Green card approvals have fallen by more than half in recent months, according to a Times analysis of agency data.

“There is no room in America for aliens who espouse anti-American ideologies or support terrorist organizations,” Joseph Edlow, the agency’s director, told Congress in February.

Critics of Mr. Trump’s approach say the administration is seeking to restrict legitimate political speech, and has conflated opposition to Israeli government policies with antisemitism.

Basing green card decisions on “ideological screenings is fundamentally un-American and should have no place in a country built on the promise of free expression,” said Amanda Baran, a senior agency official under President Joseph R. Biden Jr.

Administration officials said they were defending American values.

“If you hate America, you have no business demanding to live in America,” said Zach Kahler, a spokesman for U.S.C.I.S.

Abigail Jackson, a White House spokeswoman, said the administration’s policies had “nothing to do with free speech” and were meant to protect “American institutions, the safety of citizens, national security and the freedoms of the United States.”

The administration has moved aggressively against immigrants for expressing political views that officials have deemed anti-American, making ideology a central part of its immigration vetting process. Secretary of State Marco Rubio has revoked the visas of pro-Palestinian student activists, including one who wrote a column criticizing her university’s response to pro-Palestinian demands.

The Department of Homeland Security has proposed reviewing the social media histories of tourists seeking to visit the United States.

Immigration officers have significant discretion in deciding whether to grant foreigners long-term permanent residence. They have long considered a variety of factors, including criminal records, national security threats, family ties to the United States and employment histories.

Ideology has also traditionally been one of those factors. In some cases, U.S. law forbids officers from granting green cards to people who have belonged to a Communist or other “totalitarian” political party, have promoted anarchy or have called for the overthrow of the U.S. government by “force or violence or other unconstitutional means.”

But in the past, immigration officers have focused on statements that could incite or encourage violence, given concerns about infringing on constitutionally protected speech, former U.S.C.I.S. officials said.

The new training materials reviewed by The Times guide immigration officers through the factors they should consider when ruling on green card applications. They discourage officers from granting green cards to people with a history of “endorsing, promoting or supporting anti-American views” or “antisemitic terrorism, ideologies or groups.”

Immigration officers have been told to weigh those factors as “overwhelmingly negative.”

The documents list support for “subversive” ideologies as among other factors that could lead to an application being rejected. As an example, the materials point to someone “holding a sign advocating overthrow of the U.S. government.”

In addition, the guidance describes the desecration of the American flag as a negative factor, citing Mr. Trump’s executive order last year directing the Justice Department to prosecute protesters who burn the flag. The Supreme Court has ruled that flag burning is a form of political expression protected by the First Amendment.

Immigration officers have also been told to scrutinize applicants who encourage antisemitism “through rhetorical or physical actions.” They were instructed to “focus particularly on aliens who engaged in on-campus anti-American and antisemitic activities” after the Hamas attacks against Israel in 2023, the documents show.

Further examples in the documents of conduct characterized as antisemitic include a social media post showing a map of Israel with the nation’s name crossed out and replaced with the word “Palestine.” Another illustrative post suggests that Israelis should “taste what people in Gaza are tasting.”

Immigration officers must elevate all cases involving “potential anti-American and/or antisemitic conduct or ideology” to their managers and to the agency’s general counsel’s office for review, according to the documents.

In recent months, the agency has also changed the way it refers to the employees who adjudicate green card applications, long known as “immigration services officers.” In job postings, it now calls them “homeland defenders.”

“Protect your homeland and defend your culture,” one posting says.

Steven Rich contributed reporting.