NEW YORK (AP)- The Democrat trying to unseat popular billionaire Mayor Michael Bloomberg lobbed multiple attacks at him during their first debate Tuesday, calling him a liar and saying he spends an obscene amount of money buying votes and support for his policies.

City Comptroller William Thompson Jr. sought to portray Bloomberg as opportunistic for political moves he has made, including changing his lifelong party registration from Democrat to Republican to avoid a crowded primary in 2001 and persuading the City Council to extend the term-limits law last year so he could run again.

“At each and every level, it hasn’t been about the people of New York City, it’s been about you,” Thompson said.

Bloomberg, who has spent $64.8 million on his campaign for a third term, said he has only done what’s best for New Yorkers, and he came back at Thompson with his own attacks. Thompson, who finances his campaign by raising money, has spent about one-sixteenth of Bloomberg’s total so far.

The candidates clashed on nearly every question during the hourlong debate, which touched on issues including education, housing and how money affects political support.

Thompson accused Bloomberg, who’s a philanthropist and the richest person in the city, of buying support by donating hundreds of millions of dollars to city organizations that later back his policies.

Bloomberg, meanwhile, said Thompson is bought by special interests, referring to reports that the comptroller — whose job includes overseeing the municipal pension fund system — took campaign funds from investment managers who do business with the city.

“He says, ‘Oh, it’s separate,’ but nobody thinks it’s separate,” Bloomberg said. “Come on, nobody believes that. The bottom line is, if you want to do business with the city pension fund, you would have had to pay, and that’s wrong.”

Thompson said nobody has ever gotten a favor from his office in return for a campaign contribution, and he said it was insulting for the mayor to question his integrity.

“You should be ashamed,” Thompson told Bloomberg.

In one of many spirited exchanges, Bloomberg and Thompson argued about the failures of the nation’s largest school system when Thompson was president of the Board of Education from 1996 to 2001.

Bloomberg faulted his opponent for everything that was wrong about the city’s notoriously disastrous school system during that time.

Thompson said it’s an “apples to oranges comparison” to lay all the blame with the Board of Education president, who was one of seven members who answered to a schools chancellor. That system was dissolved, and now the schools are run by the mayor.

“I didn’t run the school system,” Thompson said. “If I was the mayor and had the $20 billion that the mayor has right now to run the school system, and had mayoral control, I would do a better job.”

There also were successes under Thompson. In 1999, the board began to end the process of automatically promoting failing students by requiring summer school. The board also ended principal tenure, and dropout rates improved during some of the years Thompson was on the board.

It wasn’t enough, Bloomberg said.

“You don’t get a medal for rearranging the deck chairs on the Titanic,” he said.

The bickering prevented either candidate from getting into details on policy, but they repeated their favorite stump slogans and arguments against each other.

In Thompson’s case, he said Bloomberg has made it harder for the middle class to afford living in the city because of higher fines, fares and fees.

The parking ticket fine was $55 for most violations when Bloomberg took office in 2002. He nearly doubled it to $105 his first year in office and raised it later to $115. Apartment rents have gone up steadily since he took office — the Rent Guidelines Board, whose members are appointed by the mayor, has approved hikes of as much as 4.5 percent some years.

And this year Bloomberg raised the sales tax by one-half percent to 8.875 percent.

The mayor has said he has made tough choices to try to revive the city’s struggling economy.

The start of the debate was briefly disrupted when someone in the audience shouted out about term limits and said, “Why are you here?”

Seizing on that energy from the audience, Thompson took more than one shot at the mayor about reversing his long-held support for the term-limits law, saying, “Mike Bloomberg lied to the people of New York City.”

Bloomberg, running on the Republican and Independent Party lines, said voters will have their say about term limits on Nov. 3 — Election Day.

Tuesday’s debate was the first of two; the other is Oct. 27.

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