By Lawrence Hurley

WASHINGTON (Reuters) - Members of the U.S. Supreme Court indicated sympathy on Monday for a Mexican immigrant's claim he should not be deported for consensual sex with his under-age girlfriend in a case heard by the justices at a time when President Donald Trump is moving to ramp up deportations.

Taking the same stance in the case as the Obama administration previously had, the Trump administration's lawyer argued that Juan Esquivel-Quintana, a lawful permanent U.S. resident who came to the country at age 12, should be subject to deportation.

Esquivel-Quintana was arrested in 2009 and convicted under California law for having sex with his 16-year-old girlfriend when he was 20 and 21 years old. The California law says it is a criminal offense for an adult to have sex with anyone under 18 when the age difference between the two is more than three years. Six other states have similar laws.

The legal fight concerns whether his conduct means he is subject to deportation under federal immigration law, which says any immigrant convicted of "sexual abuse of a minor" can be deported.

During the one-hour oral argument, several of the eight justices, including liberals Elena Kagan and Stephen Breyer, indicated they believed Esquivel-Quintana's actions did not fit within the definition in the immigration law.

One of the issues before the justices is whether to embrace the interpretation of the law adopted by the federal Board of Immigration Appeals, which ruled against Esquivel-Quintana.

Esquivel-Quintana's lawyer, Jeff Fisher, said the justices should instead take into account that his client's actions would not be illegal based on laws in 43 states. Federal criminal law defines "sexual abuse of minor" as a crime in which the victim is under 16 and the defendant at least four years older.

Liberal Justice Elena Kagan appeared to agree with Fisher, saying the government wants to ignore all the state laws and the federal law and conclude independently that "we just know that when somebody talks about sexual abuse of a minor, they're talking about age 18 with a three-year-differential."

Justice Anthony Kennedy, a conservative who sometimes sides with the liberal justices in key cases, also indicated skepticism about deferring to the government's interpretation, noting that the Board of Immigration Appeals has no special expertise on criminal law.

Lawyers for the Trump administration took over Esquivel-Quintana's case from the administration of President Barack Obama after the Supreme Court agreed to hear his appeal of a January 2016 ruling by the Cincinnati-based 6th U.S. Circuit Court of Appeals in favor of the government.

In arguing that Esquivel-Quintana should be subject to deportation, the Trump administration's lawyer, Allon Kedem, told the justices, "We point to legislative history, which is relatively sparse, but I think it strongly indicates that Congress wanted to get a lot tougher on crimes involving children."

The Trump administration got some support during the argument from conservative Justice Samuel Alito, who said it would be a "meaningless quest" to try to come up with a single definition for "sexual abuse of minor" based on all the different state laws.

The Trump administration has announced plans to increase deportations and broaden the categories of immigrants targeted.

(Reporting by Lawrence Hurley; Editing by Will Dunham)