President Carter returned to his home here today and spent an hour and a half walking along Main Street greeting friends and several hundred tourists.

Looking rested after eight days of vacation on Sapelo Island off the Georgia coast, the president refused to discuss substantive issues, telling reporters he still considered himself on vacation.

During the tour of shops along Main Street, which has become almost ritual whenever Carter returns to Plains, the president said that his brother Billy, plans "to spend the night with us this coming weekend." Billy Carter is scheduled to be released next week from an alcoholic rehabilitation unit at a naval hospital in California.

Carter, his wife Rosalynn, son, Chip, and grandson, James Earl Carter IV, flew by helicopter from Sapelo Island and arrived here early this afternoon.

The president and his wife stopped for about an hour at their home, and then headed for the Plains tour, departing from the usual ritual to walk the three blocks from their home to Main Street rather than be driven. Along the way, they stopped to chat with neighbors and were soon surrounded by a crush of people, including tourists, reporters and photographers.

The president visited more than half a dozen Main Street establishments, including the post office, the bank, a clinic, a hardware store and his cousin Hugh Carter's antique shop. He spent about five minutes in each, inquiring about the townspeople and looking at displays of photographs of himself and his family.

Carter's last shop on the tour was the Carter peanut warehouse, his family business, where he chatted with employes and sat quietly on a stool looking around the warehouse office.

the President told friends in Plains that he enjoyed his eight days on secluded Sapelo Island, remarking that it was good to be "all by ourselves."

Carter remained here overnight. He is scheduled to fly Saturday to Calhoun to attend the christening Sunday of his granddaughter, Sarah Rosemary. He is due back in Washington Sunday night. CAPTION: Picture 1, President, at home in Plains, savors black walnut ice cream downtown. AP; Picture 2, Still on Georgia vacation, the chief executive is greeted after 'copter landing.UPI