FORT WORTH, Texas (AP) _ The Fort Worth Art Museum has acquired 10 related works by American painter Robert Motherwell, and the artist himself is participating in the selection.

The paintings include a major 7-by-10-foot 1981 painting called ''Stephen's Iron Crown,'' purchased with funds provided by the Sid W. Richardson Foundation of Fort Worth, museum Director E.A. Carmean Jr. said.

Nine smaller paintings were acquired as a joint museum purchase and gift of the artist, known as a pioneer in the post-war Abstract Expressionst movement.

''What is so exceedingly rare in this grouping is the active role of Mr. Motherwell in selecting these pictures and articulating their interconnections,'' Carmean said.

The museum would divulge no purchase price, but experts estimate the value of the 10 works at $500,000 to $750,000.

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SANDRINGHAM, England (AP) - Four of the queen's horses got a royal tongue- lashing from Prince Philip, Queen Elizabeth II's husband, after the carriage he was driving in a horsemanship contest went astray.

Reporters at the Norwich Union Trials heard Philip shout ''You bloody twits 3/8'' Saturday after the team galloped to the wrong side of an obstacle on the course in this east England city.

On the second go-round, the prince negotiated the course successfully. But the 64-year-old ex-seaman, known for his salty language, was overheard mumbling, ''You're a useless lot.''

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PLAINS, Ga. (AP) - When Jimmy Carter pitched a softball team composed of former administrative aides to victory, he joked that the win boosted his record to 1-43.

''This is the first victory of my lifetime,'' said the former president, 61.

Saturday's game in Carter's hometown was part of a Labor Day weekend reunion of more than 200 former administration officials and other guests. Jody Powell, Carter's White House press secretary, had organized the get- together, which also featured a fish fry and barbecue.

Powell said the key to Carter's 9-7 success was his - Powell's - leaving the game in the seventh inning.

Sam Donaldson, ABC's White House correspondent who played on the opposing team, said he hit solid balls each time and had unlucky breaks.

''He figured some technical way to get me out,'' said Donaldson. ''Of course, he did that all during his presidency.''

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WARM SPRINGS, Ga. (AP) - Donna Cline of Las Vegas, Nev., was crowned Ms. Wheelchair America 1986 during the 14th annual pageant, held at the Roosevelt Warm Springs Institute for Rehabilitation.

''I couldn't believe it,'' Ms. Cline said after Saturday's pageant. ''All of these women are so accomplished in their own right that they all deserve the crown.''

Ms. Cline, 26, is a news anchor and reporter for KVBC-TV in Las Vegas. She is a paraplegic as the result of a 1978 automobile accident.

Denise Weisenborn of Maple Heights, Ohio, was selected first runner-up. She is an attorney who uses a wheelchair because she has muscular dystrophy.

Ms. Cline will spend the next year traveling to promote the pageant program and as an advocate for the more than 36 million disabled people in the United States.

Contestants from 14 states and Puerto Rico competed in the pageant. They were judged on their accomplishments, personality and appearance.