Nine-year-old Jason Ellsworth did a little singing and a whole lot of heart-stealing at the White House yesterday morning. Jason, who has cerebral palsy and has been blind since birth, sat at the East Room piano and, supported by the harmonies of the Gatlin Brothers, launched into Hank Williams' "Long Gone Lonesome Blues," complete with some precocious yodeling.

The country music aficionado's spirited reading earned a standing ovation (he got one at the Grand Ole Opry, too), and affirmation when he queried, "Don't I get to do another one?" in a drawl that belied his Connecticut roots. Cradling Jason in his arms, Larry Gatlin carried him over to a chair and invited him to sing harmony to "All the Gold in California."

Afterward, Gatlin quipped, "We've decided we're getting him a shaving kit and jeans and taking him on the road."

"I sang that like Ray Charles, I'll tell you that," Jason replied.

"If anybody got through that entertainment with a dry eye, they did better than I," a moist-eyed Nancy Reagan said at the program's end. She had invited Jason and other young artists to perform at the White House to kick off "Inspire '85," a week-long showcase of the artistic, athletic and educational achievements of disabled persons. All the performers are participants in "Very Special Arts," a program affiliated with the Kennedy Center.

Mrs. Reagan and actor Cliff Robertson welcomed Jason and the Gatlins, Jermaine Jackson (who joined the Louisiana Very Special Arts Quintet on "I Just Called to Say I Love You" and a song about motherhood dedicated to the first lady) and comedian-actress Geri Jewell, who has cerebral palsy.

"Everyone deserves a chance to become all they can, and being disabled doesn't mean you're handicapped," Mrs. Reagan said after the program. "So many of you here today are shining examples of that."

William Britt, a mentally retarded artist from New York, joined with White House press secretary James Brady, who walked slowly with the aid of a cane because of the injuries he received during the attempted assassination of Ronald Reagan in 1981, to present an oil painting of the White House in recognition of Mrs. Reagan's work with the disabled.

Robertson, whose most memorable film role was as a mentally retarded bakery worker in "Charly," said that "Inspire '85" is dedicated to the 35 million Americans who are disabled.

"We've all seen the victories that these remarkable people have made in our country, the accomplishments of people said to be handicapped, people who triumph by concentrating on their assets, talents, skills, courage, enthusiasm, perseverance, cheer, hard work. Today we celebrate their achievements in the arts, education and sports."

The five-day event, which involves more than two dozen government agencies and private organizations, is coordinated by the President's Committee on the Handicapped and the People-to-People Committee on the Handicapped. An international forum bringing together more than 300 national and international leaders will be at the L'Enfant Plaza Hotel through Thursday. Friday and Saturday "Inspire '85" moves to the Mall with demonstrations, exhibits and activities to focus attention on the gains the disabled have made in the community, workplace and home.