John N. Mitchell, the last Watergate criminal to go to prison, yesterday was granted a parole beginning Jan. 19. He will have served 19 months of his 1-to-4-year sentence, counting a five month medical furlough.

The former attorney general, a one time law partner of Richard M. Nixon and Nixon's manager in two winning presidential campaigns, will be 65 in September. This year, while on medicial furlough, he underwent major surgery for repair of a weakened artery in his abdomen and for replacement of an arthritic right hip.

The U.S. Parole Commission, after a July 5 interview with Mitchell, apparently accorded little weight to his age and infirmities since the length of his sentence is similar to that of his two co-defendants, H.R. Haldeman and John D. Ehrlichman, whose time in prison was set at 18 months each.

When Mitchell entered the minimum-security prison at Maxwell Air Force Base in Alabama on June 22 last year he was under a 2 1/2-to-8 year sentence, the term also assessed codefendants, Haldeman and Ehrlichman. but last October, U.S. District Court Judge John J. Sirica reduced the sentences of all three men to 1-to-4 years.

After fighting his conviction to the Supreme Court, Mitchell was the last of 25 men sentenced to prison in Watergate to begin serving his term. The parole commission has already ordered a Dec. 20 release for Haldeman, who entered prison at Lompoc. Calif., a day before Mitchell. At that time, Haldeman will have served 18 months, the same as Ehrlichman, who completed his time at Stafford, Ariz., in April.

Haldeman was Nixon's chief of staff and Ehrochman was in charge of the White House.

Mitchell resigned as attorney general on March 1, 1972, to take charge of the relection campaign and quit four months later-two weeks after agents of the reelection committee were arrested in the Watergate break-in.

All three men convicted of conspiring to obstruct justice, obstructing justice and lying under oath in trying to hide White House involvement in the aftermath of Watergate. Nixon was named by a grand jury as one of 18 co-conspirators but no charges were lodged against him.

Mitchell was accused by his reelection committee assistant, Jeb Staurt Magruder, of having authoriedz the spending of $250,000 for political intelligence gathering-specifically including the break-in at Democratic Party headquarters in the Watergate office building.

Mitchell always denied that. He was convicted of lying when he said under oath he knew nothing about illegal intelligence gathering, and that he didn't know reelection committee lawyer G. Gordon Liddy had admitted the burglars were his agents, and that he didn't order destruction of the intelligence gathering files.

In recent weeks Mitchell has progressed from walking with crutches to using a cane. He works in the institution's education section and for a time was a clerk in the library. Like many others involved in Watergate, Mitchell has been working on a book.