SALT LAKE CITY, DEC. 9 -- The kidnaped son of a wealthy businessman was rescued unharmed today, but an FBI agent was stabbed in the chest by one of two teen-agers who had demanded $1 million ransom, authorities said.

The suspects were believed to be high school classmates of James Huntsman, 16, who was abducted at knifepoint from the driveway of his home by two masked males Tuesday night, Police Chief Bud Willoughby said.

His father, Jon M. Huntsman, is chairman and president of Huntsman Chemical Corp., the nation's largest privately held chemical company, and held offices in the Nixon administration.

FBI agent Grant Alan Jacobsen was in serious but stable condition after being stabbed by a teen-ager who had brought the young Huntsman to a pay phone to talk to his father, authorities said.

Another agent tackled the fleeing assailant, who was arraigned in federal court on a charge of assaulting a federal agent, Willoughby said.

The other suspect was arrested hours later at Highland High School, Willoughby said. State kidnaping charges will be filed in juvenile court against the suspects, Willoughby said, declining to identify them. He said authorities may seek to have the youths tried as adults.

The abduction had been plotted for more than a week, Willoughby said, but officials would not give more details. "Our son is now recovering, as are other family members, from this terrible ordeal," said the youth's father.

He said the kidnapers had demanded in a telephone call to his home early today that he pay $1 million, $100,000 in used $100 bills.

"I indicated to the abductors I would not proceed until I spoke to our son," Huntsman said.

The younger Huntsman was later brought to the pay telephone at a supermarket and talked to his father just before the agents closed in, Bryant said.

Huntsman served in the U.S. Department of Health, Education and Welfare in 1970 and as special assistant to President Nixon in 1971-72.