Governor Huckabee says he plans to commute the sentence of a man serving life in prison for committing murder and battery more than 25 years ago. The state parole board recommended the commutation for Robert A- Arnold Junior after one of his victims wrote the board on his behalf. The filed notice of intent yesterday of his plans to commute Arnold`s sentence. The governor`s notice began a statutory 30-day period for public comment before a final decision on commutation can be made. If Huckabee`s decision becomes final, Arnold would be eligible for parole immediately. Arnold, now 47, pleaded guilty to first-degree murder in 1977 in Hempstead County in the shooting death of his father-in-law, Douglas Fowler. He pleaded guilty to first-degree battery in the shooting of Fowler`s wife Marte. Marte Fowler, who now lives in Texarkana, wrote letters to the board on Arnold`s behalf. She said yesterday that she had forgiven her former son-in-law.