The jury in the Alan J. Arnone murder trial was sent home by an Arlington circuit court judge last night after deliberating almost four hours yesterday without reaching a verdict.

Arnone, a 24-year-old Maryland man, is accused of robbery and murder in the slaving of Ronald J. Pettine, a former political aide to Rep. Morris Udall who was found bludgeoned to death at Iwo Jima Memorial in October 1976.

Two other men, Michael G. Simoneau, 18, of Falls Church and Charles A. Bamman, 22 of Arlington, are already serving prison sentences in connection with the slaying.

In closing arguments yesterday, William D. Dolan, Arnone's attorney, portrayed the four-foot nine-inch defendant, as a "follower, a tag-along with any group that would have him because no one else would. He was the parrot on the shoulder of the pirate, a mascot for Simoneau and Bammon."

Assistant Commonwealth's attorney Kenneth Melson countered, telling the jury Arnone had "been to (Iwo Jima) before, he knew what was happening, and he struck the victim. He is not a parrot, he is an individual and he knew what he was doing."

The jury is scheduled to resume its deliberations this morning.