Two hours after a grand jury indicted Arizona Gov. Evan Mecham late Friday for campaign fraud, the office of an attorney investigating grounds for the governor's impeachment was damaged by arson.

Fire officials, who continued their search yesterday for clues in the blaze, said documents amassed by Phoenix lawyer William French in an impeachment probe were in another area and not damaged.

Officials said the file-room fire, extinguished by a sprinkler, was arson. But they had no indication that it was related to the controversy that has swirled around a year-old governorship that has seemed to go from worse to worse.

Mecham, a wealthy automobile dealer, took office a year ago after winning a divisive three-way campaign. At his inauguration he promised a visionary "new beginning" that instead has become a bumpy political hayride reminiscent of the best that the brothers Long of Louisiana could conjure.

The state grand jury indictment was the latest in a series of incidents that catapulted Mecham onto newspaper front pages around the country, touched off a recall campaign and led the state House of Representatives to consider impeaching him.

His tart commentaries on race, sex and religion have infuriated blacks, women, homosexuals, Hispanics and Jews and have led more than 240,000 Arizonans to sign petitions attempting to force a recall election. His appointments have stirred more criticism.

The embattled 63-year-old Republican governor, meanwhile, defiantly rejected new calls for his resignation after the six-count indictment charged him with fraud and perjury in connection with a secret $350,000 contribution to his 1986 campaign. Mecham faces arraignment Jan. 22 and, if convicted, he would be removed automatically from office.

Mecham said through a spokesman that he intends to go ahead Monday with his scheduled State of the State address to the House, where fellow Republicans have joined the chorus calling for him to vanish into the desert sun.

Mecham later read a statement in the Capitol lobby declaring himself "completely clean." The Associated Press quoted Mecham as saying that "a swirl of manipulation, deceit and skulduggery" was being used in an effort to "overthrow a constitutionally elected official." He refused to answer questions.

Mecham's dwindling support in the state legislature, which Republicans control, continued to wane. Moderates remained divided over a Mecham resignation, but conservatives voiced fears that Mecham's peccadilloes could give Democrats a majority in one chamber or the other for the first time since 1974.

The Arizona Republic, the state's largest newspaper, said in an editorial yesterday that the indictment had destroyed Mecham's ability to govern.

Mecham's press secretary, Ken Smith, was quoted by the Associated Press as saying that the governor was not surprised by the indictment and that he felt "a sense of relief because at least this formalizes some of this . . . . There's no longer jousting at windmills."

Mecham and his brother-campaign treasurer, Willard, who was also indicted on three similar counts, were charged with concealing a $350,000 campaign loan in November 1986 by Barry Wolfson, a Tempe developer. The loan made up about a third of his funds when Mecham was elected on his fifth try for the office.

The governor, denying any wrongdoing, blamed his brother for "an honest mistake." After reporters uncovered the loan, Mecham amended his official personal and campaign financial documents.

The Mechams were charged with perjury, fraud and false filing for omitting the loan from a campaign-finance disclosure. The governor also was charged with fraud and two counts of perjury for failing to report the loan on his personal financial disclosures.

All nine counts in the indictments mentioned the Wolfson loan. The loan was not itemized on a campaign report filed by Willard Mecham, as required by law. It was lumped instead with a list of other small contributions. Evan Mecham signed the report in February 1987, a month after assuming the governorship.

The governor asked Wolfson in a letter to keep the loan confidential. Wolfson said that he never asked that the contribution be withheld from Mecham's financial reports.

The indictments came a day after Evan Mecham had gone through a second day of grand jury interrogation regarding the campaign loan.

State House Speaker Joe Lane, also a Republican, said the indictment will have no effect on consideration of whether to impeach Mecham over the loan. Attorney French, appointed by the chamber to study the issue, is scheduled to deliver his report Friday.

Ed Buck, founder of the Mecham Recall Committee, indicated that he would rather avoid a new election.

Mecham jumped into political hot water in his first week in office. He abolished a state holiday honoring the Rev. Martin Luther King Jr., declaring that it had been illegally enacted by Bruce Babbitt, his Democratic predecessor. Mecham stirred the pot more by later questioning whether the slain civil rights leader merited a holiday.

The backlash was immediate. The state lost millions of dollars as various organizations canceled Arizona conventions in protest of Mecham's abolishment of the state holiday.

But there was more to come, as Mecham found ways to offend almost every group in the political spectrum. He said he found the pejorative "pickaninny" a term of affection. He said working women were a cause of high divorce rates. He called a reporter a "nonperson" and refused to answer his questions.

He worried that he would not know what to say when Pope John Paul II visited the state, since he was unaware if he spoke English. After Buck, who is gay, started the recall campaign, Mecham blamed it on "militant liberals and the homosexual lobby."

His most recent contretemps enraged Jews. The governor, a Mormon, told a synagogue breakfast group that the United States is a "great Christian nation" and that Jesus Christ is "Lord of the land." Mecham later told reporters he meant that since the United States was founded by Christians and was thus a Christian country.

The rabbi who had invited Mecham to speak called the governor's remarks a "travesty . . . extremely insulting." Another Jewish leader said Mecham was insensitive to concerns of the Jewish community.

Pish tosh, the governor retorted. "I am not at all insensitive." The proof: His lawyer is Jewish and he has "many good Jewish friends."