Lamar Alexander was sworn in as governor of Tennessee tonight, three days before his scheduled inauguration, to prevent outgoing Gov. Ray Blanton from commuting the sentences of any more prisoners, he said.

The surprise swearing-in came as reports grew that a grand jury would investigate the pardons or commutations granted to 52 prisoners by Blanton Monday night.

Shortly before he took the oath of office, Alexander said, "I have been authorized by the lieutenant governor and the speaker of the House to make this statement:

"The U.S. attorney today advised each of us that he has substantial reason to believe that the governor of Tennessee was planning to release one or more persons from prison who are targets of an investigation of pay-offs for release from prison."

Alexander said he had been assured the early inauguration, apparently without precedent in Tennessee, is legal. The state attorney general's office had given an opinion earlier in the week that it was legal for Alexander to take office any time after Jan. 15.

"These are not very happy days for the state of Tennessee," Alexander said, "and these are not very happy days for me."

Alexander said he was notified at 4 p.m. that the ceremony had been scheduled. It took place at 5:56 p.m.

State Atorney General William Leech said that five minutes before the ceremony, he called Blanton, who was at his private residence, and said, "'Governor, this is General Leech. I just wanted to call you myself and let you know that in a few minutes, Lamar Alexander will take the oath of office.'"

Leech said there was a pause. "I would not want to paraphrase what he said," Leech said. "He was hurt. He said he hated to go out of office like this.He said, 'I accept it and I acknowledge your message.'"

Blanton ordered commutations or pardons for 24 convicted murderers and 28 other prisoners, and by this evening 10 murderers and two armed robbers had been released.

Alexander said he would act to keep any others from being released.

Blanton acted a month after three state employes, including two members of his office legal staff, were arrested by the FBI and charged in a federal complaint with extortion and conspiracy to sell pardons, paroles and commutations.

A federal prosecutor, who asked not to be identified, said the grand jury may investigate the 49 commutations and three pardons granted by Blanton.

In the wake of the pardons and commutations, citizen outrage over the release of the prisoners had raised concern for Blanton's safety at the inauguration.

Of the three prisoners pardoned, one had been convicted of murder. Of the 49 whose sentences were commuted, 30 had their sentences reduced to the time they had already served, making them eligible for immediate release, including 17 who had been convicted of first or second-degree murder.