Arlington National Cemetery officials yesterday replaced the wooden cross stolen this weekend from the grave of Sen. Robert F. Kennedy with the cross that originally marked the grave.

Cemetery guards discovered Sunday that a redwood cross and modest marble tombstone marking Kennedy's grave were missing. Police speculated that one or more thieves scaled a stone wall and a six-foot fence surrounding the 600-acre cemetery and then dug out the one-by-two-foot Vermont marble marker and uprooted the two-foot wooden cross.

The cross was replaced yesterday morning, and cemetery officials will replace the tombstone by the end of the week.

"The original pine cross that was placed on the grave right after Kennedy was buried in 1968 was replaced with a redwood one in 1970," said cemetery superintendent Raymond J. Costanzo. "We had the original one in storage and just put it back."

Park police said they still have no leads in the theft. Costanzo, who has been cemetery superintendent for 10 years, said the grave-marker theft is the first he remembers.

The senator's grave is on a hillside about 25 yards from that of his brother, President John F. Kennedy.

The cemetery is patrolled by Army personnel during the day, and Park Police make patrols of the grounds after the iron cemetery gates are locked at night. Costanzo said he plans to meet with Army officials to discuss whether additional security measures are needed at the cemetery.