President Reagan signed legislation yesterday creating a national historic site in Plains, Ga., the home town of former president Jimmy Carter. The law authorizes the National Park Service to spend up to $3.5 million to "preserve the key sites and structures associated with Jimmy Carter during his lifetime, to provide for the interpretation of his life and presidency and to present the history of a small Southern town."

It also creates a 650-acre national preservation district in and around Plains and authorizes the park service to acquire by donation or purchase preservation easements on the historically or culturally significant buildings or open spaces in the area. So far, the Carters have agreed to donate their home, and the trust is raising money to buy Carter's boyhood home.

Legislation creating a Carter historic site was first introduced in Congress in 1983 by Rep. Richard Ray, a Democrat from Perry, Ga., whose district includes Plains.

No Santa for Claus

Claus von Bu low, cleared of charges he tried to kill his wife, has agreed to divorce his comatose spouse and renounce his claim to the $25 million he would have inherited upon her death.

Von Bu low confirmed yesterday that he has reached an out-of-court settlement with his stepchildren, but declined to discuss the details of the deal with the media as that was "part of the agreement."

Michael Armstrong, a lawyer for the stepchildren, said: "Claus is out of everything. The only thing he gets to keep is personal property he could affirmatively prove he brought to the marriage, such as furniture and paintings."

In return for von Bu low's agreement, sources close to the litigants told the New York Post, the couple's only child, Cosima, will inherit one-third of the $100 million estate left by Sunny von Bu low's mother.

In 1985, a Rhode Island Superior Court jury acquitted von Bu low of charges he tried to kill his wife with insulin injections. But Sunny von Bu low's two children from her first marriage insisted he was culpable and filed a $57 million suit against him.

Wallace Resting After Tests

Former governor George C. Wallace, 68, was released from a hospital in Montgomery, Ala., a few hours after he underwent tests because of complaints about chest pains, his son said yesterday.

State Treasurer George Wallace Jr. said the former four-term governor was taken by ambulance to the hospital Tuesday morning. "He's had so much pain for so long -- abdominal pain he's been dealing with," the younger Wallace said. "But when he had chest pains, I think it worried him."

Wallace was released Tuesday after tests revealed no blockages or other heart problems, his son said, adding that his father was resting at his Montgomery home.

The elder Wallace has been in and out of hospitals in recent years, often because of complications from paralysis he has suffered since his spinal cord was damaged by a would-be assassin's bullets in 1972.

Ebert and Siskel Rate the Movies

Chicago film critics Roger Ebert and Gene Siskel have gone thumbs-up with a preview of their year-end Top 10 picks. Ebert's choices are Mel Gibson's police thriller "Lethal Weapon" and Woody Allen's nostalgic comedy "Radio Days" as the year's best flicks. Siskel gives highest marks to "Roxanne," a modern rendition of the classic "Cyrano de Bergerac" in which Steve Martin plays a fire chief who falls for a beauty played by Daryl Hannah. Siskel's second place goes to "Moonstruck," a just-released film in which Cher's character falls in love with her fiance''s brother.

Chuck Conconi is on vacation.