WASHINGTON, June 28 (Reuters) - The U.S. Supreme Court on Monday extended gun rights to every state and city in the nation in a ruling involving Chicago's 28-year-old handgun ban.

By a 5-4 vote and splitting along conservative and liberal lines, the nation's highest court extended its landmark 2008 ruling that individual Americans have a constitutional right to own guns to all the cities and states for the first time.

The right to bear arms, under the Second Amendment of the U.S. Constitution, previously applied to just federal laws and federal enclaves, like Washington D.C., where the court struck down a similar handgun ban in its 2008 ruling.

Gun rights have been one of the country's most divisive social, political and legal issues. Some 90 million people in the United States have an estimated 200 million guns.

The United States is estimated to have the world's highest civilian gun ownership rate. Gun deaths average about 80 a day, 34 of them homicides, according to U.S. government statistics.

The ruling, issued on the last day of the Supreme Court's term, was a victory for four Chicago-area residents, two gun rights groups and the politically powerful National Rifle Association.

It was a defeat for Chicago, which defended its law as a reasonable exercise of local power to protect public safety. The law and a similar handgun ban in suburban Oak Park, Illinois, were the nation's most restrictive gun control measures.

"We hold that the Second Amendment right is fully applicable to the states," Justice Samuel Alito concluded for the court majority in the 45-page ruling. (Reporting by James Vicini, Editing by Vicki Allen)