PHOENIX, FEB. 29 -- Beginning his defense of Gov. Evan Mecham (R) after less than a week's preparation, veteran defense attorney Jerris Leonard lectured the Arizona Senate today for holding Mecham to "a standard . . . that hasn't been applied to others and . . . doing it in a court of impeachment."

The charges against Mecham -- failing to report a $350,000 campaign loan, lending $80,000 in office funds to his auto dealership and trying to thwart an investigation into an aide's alleged death threat against a grand jury witness -- say little about his capacity to govern, Leonard insisted.

"He hasn't dipped his hands into public funds," he said, his amplified voice thundering across the paneled Senate chamber on the first day of a trial that is expected to last at least two months. "He hasn't ripped off the treasury."

Leonard, a former Wisconsin state legislator and former official in the Nixon administration Justice Department, materialized last week as the new head of the Mecham legal team, further complicating a chaotic political situation.

He has indicated that he will ask a federal court to delay the Senate proceedings until after Mecham's criminal trial on fraud and perjury charges -- and he told the Senate several times today that it would be better off leaving the governor alone for a while.

Leonard has defended Florida motivational entrepreneur Glenn Turner, Chicago racketeer Allen Dorfman, boxing champion Muhammad Ali and former president Gerald R. Ford's campaign manager, Howard H. (Bo) Callaway. He resigned from the influential Washington law firm of Manatt, Phelps, Rothenberg and Evans last week when his partners objected to his taking Mecham's case.

The lawyer he replaced, Phoenix attorney Murray Miller, today gave the Senate a sometimes emotional account of his dismissal and suggested that Leonard had not had time to absorb "bushels and bushels" of legal documents generated by the three-pronged legal and political assault on the 63-year-old governor.

Although he asked the Senate to postpone its trial, Leonard said he was ready to proceed. Mecham called an afternoon news conference to express his "disappointment" at Miller's "prejudicial and grandstanding" behavior and his confidence in Leonard.

The 29 senators, missing one colleague because of illness, repeatedly rejected Leonard's requests that they dismiss the charges as insufficient for trial or delay at least part of the trial. In a series of votes, Mecham received no more than seven in his favor, and only two senators supported him consistently.

The Senate did agree to consider the unreported-loan charge, the only issue in his criminal trial, last.

Often Leonard spoke in a friendly manner, reminding his audience that he was once a state legislator and knew their problems. Then he lashed out at the Senate's insistence on forcing Mecham into two trials that could overlap. "If that is the posture you want to be in, Senator, then that is up to you," he shouted at Sen. Robert B. Usdane (R-Scottsdale).

By afternoon, Leonard had to enter a "not guilty" plea on Mecham's behalf to the 23-count bill of impeachment passed 46 to 14 by the state House.

Mecham did not attend the Senate session, presided over by state Supreme Court Chief Justice Frank X. Gordon, and said he did not watch it on television. "I was busy," he said. "I have a lot of other things to do."

Since his impeachment and temporary removal from office Feb. 5, Mecham has retreated to the huge, modern ranch house he owns in the suburb of Glendale.

Mecham is fighting on three fronts: in the Senate, which could convict him and bar him from future office ; in court, where a conviction could remove him from office and send him to jail, and at the polls, where he has vowed to run in a May 17 recall election against Carolyn Warner, the Democrat he beat in a three-way 1986 race, and former U.S. representative John J. Rhodes (R).

The May 17 election date makes timing critical to his Senate defense, since he could win another three-way race despite his troubles. The state is obligated by law to pay a "reasonable" share of his campaign expenses and his support remains strong among rural, blue-collar Arizonans suspicious of the political establishment arrayed against him.

If the Senate trial is delayed until after the recall election, and the criminal trial runs late or ends in acquittal, Mecham could win the recall election and then put heavy pressure on the Senate to drop its charges. Mecham supporters, planning a fund-raising rally Wednesday night, noted that even if the Senate convicts him, it would have to vote again to bar him from future office and might be unwilling to go that far.