President Reagan began a Thanksgiving vacation at his California ranch today and introduced his sheep dog, Lucky, to her new home at his 688-acre spread in the Santa Ynez mountains.

The president, with the year-old, 65-pound dog on a leash, appeared before reporters on Air Force One and announced that Lucky was about to be admitted to "dog heaven -- 688 acres -- won't have to have a leash on her."

Reagan brushed aside questions about congressional tax and farm bills on which he faces decisions when he and Congress return to Washington next week. "I'm concentrating on dog heaven," he said.

As he approached reporters flying with him to California, with the dog at his side, Reagan joked, "I get good reviews, or I turn her loose!"

Lucky arrived at the White House as a weeks-old puppy after being given to Nancy Reagan by a March of Dimes poster child last December and has lived there since then. The president said he will miss Lucky in Washington but would "talk 'em into more trips to California." This is Reagan's fourth trip here this year.

The first lady plans to join the president at the ranch Wednesday after visiting her mother in Phoenix and traveling elsewhere in California. She has urged aides to give her husband time to rest after last week's Geneva summit.