Mario Montuoro had every reason to think life's odds were stacked against him--until he flicked on the news Saturday.

In recent months, Secretary of Labor Raymond J. Donovan has denounced him as "a damnable and contemptible liar" and reports circulated that organized crime had put a price on Montuoro's head.

But Saturday he found out from New York's Channel 5 he might be a state lottery winner. Yesterday he found out he had won precisely $2 1/2 million.

"You got to start from the bottom and go up," Montuoro philosophized. Literally.

The unemployed dynamite blaster--an ousted union official who triggered the current investigation of Donovan--helped excavate the hole in Manhattan that made room for the World Trade Center.

Yesterday he went back there, to the 65th-floor offices of the lottery regional director, James Nolan, who confirmed the six winning numbers Montuoro had heard rattled off on television.

"Mario will be our 67th millionaire," Nolan said. "He told us he wants to pay back the welfare checks he got, too. I said, 'Very good. The city needs the money.' "

Monturo, 49, says he's determined to win his fight for reinstatement in his old union, Laborers Local 29, where he was secretary-treasurer and assistant administrator of the pension fund. He was fired in 1978. In January an administrative law judge for the National Labor Relations Board ordered Montuoro reinstated with back pay.

He's still waiting.

"I still want my back pay and my job, even if I have to keep my chauffeur and limousine waiting outside for me all day," he said.

Montuoro bought his winning ticket Thursday at a candy store in the South Bronx. It was one of eight tickets he buys every week for $4. He could have won $5 million, but lottery officials said an aspiring actor from Brooklyn picked the same six numbers and will share the prize.

Montuoro--who counts his wife, Karen, two stepchildren, an older son and "five adopted lawyers" in his household--will collect $117,000 in two weeks, the first of 21 annual installments.

The investigation of Donovan, whom Montuoro accused of witnessing a $2,000 payoff, goes on. Meanwhile, Montuoro will be busy shopping. His 10-year-old stepdaughter, Jennifer, wants a new bed with a canopy.