Jan 18 (Reuters) - U.S. Supreme Court justices on Tuesday appeared inclined to rule in favor of a Christian group that sued on free speech grounds over a refusal by Boston officials to fly a flag bearing the image of a cross at City Hall in a challenge backed by Democratic President Joe Biden"s administration. The justices heard oral arguments in an appeal by the group, Camp Constitution, and its director, Harold Shurtleff, over Boston"s 2017 denial of their application to raise the Christian cross flag due to concerns that it could appear as an unconstitutional government endorsement of a particular religion. Lower courts sided with the city. The Supreme Court, which has a 6-3 conservative majority, has taken an expansive view of religious rights and has been increasingly receptive to arguments that governments are acting with hostility toward religion. The dispute arose over Boston"s practice of allowing private groups to hold flag-raising events using one of three flagpoles on the plaza in front of City Hall to promote inclusion and the diversity of the city"s residents. From 2005 to 2017, Boston approved all 284 applications it received before rebuffing Camp Constitution. The vast majority of flags were those of foreign countries, but also one commemorating LGBT Pride in Boston. At issue is whether the flagpole became a public forum meriting free speech protections under the U.S. Constitution"s First Amendment to bar discrimination based on viewpoint, as the plaintiffs claimed, or whether it represented merely a conduit for government speech not warranting such protection, as Boston claimed. Liberal and conservative justices questioned the city"s stance. Liberal Justice Elena Kagan doubted that in this particular case the cross flag could violate the First Amendment"s so-called establishment clause prohibiting the government from establishing a state religion. "In the context of a system where flags go up, flags go down, different people have different kinds of flags, then it is a violation of the free speech part of the First Amendment and not an establishment clause violation - the end," Kagan told a lawyer for Boston. Conservative Justice Samuel Alito noted that Boston"s policy appeared to exclude flags that were discriminatory, offensive or religious. "When you say anybody can speak by putting up a flag, with these few exceptions, are you not creating a forum for private speech rather than speaking your own mind?" Alito asked a lawyer for Boston. But liberal Justice Sonia Sotomayor voiced concern about the potential for confusion by average observers, saying it is a "fiction" that people would think a raised flag outside City Hall relates to an event not sponsored by the city. "If you see a flag on the pole, you think it"s City Hall speaking," Sotomayor said. Camp Constitution, whose mission is "to enhance understanding of our Judeo-Christian moral heritage" as well as "free enterprise," sued in 2018 over its rejection. Among other topics, Camp Constitution"s website posts materials questioning the effectiveness of COVID-19 vaccines, claiming that last year"s U.S. Capitol attack was actually a cover up for "massive" 2020 election fraud and calling Japan"s 1941 Pearl Harbor attack and al Qaeda"s Sept. 11, 2001, attacks on the United States "carefully orchestrated false flags." The Boston-based 1st U.S. Circuit Court of Appeals ruled that the city"s control of the flag-raising program made it government speech. Biden"s administration backed Camp Constitution in the case, arguing in court papers that because Boston treated the flagpole as a forum for private speech it cannot approve "private civic and social groups while excluding otherwise-similar groups with religious views." Boston said that requiring it to open the pole to "all comers" could force it to raise flags promoting division or intolerance, such as a swastika, or a terrorist group. Given that risk, Boston last October halted applications to use the flagpole, at least while the case plays out. Biden"s administration and some justices said Boston could create and closely control a more limited flag-raising program going forward to avoid those concerns.