After a summer of lawsuits and tabloid headlines, the New York Knicks wanted to get back to basketball.

So much for that plan.

The team fined Stephon Marbury more than $180,000 after he blew off last night’s game against Phoenix, the latest clash between the disgruntled point guard and coach Isiah Thomas.

The Knicks sent Marbury a letter informing him of the fine, according to a person with knowledge of the penalty. He requested anonymity because he wasn’t authorized to discuss it. The Knicks would not confirm the fine.

The Knicks wouldn’t say if Marbury would attend tonight’s road game against the Los Angeles Clippers, or if they would fine him again if he doesn’t show.

According to the NBA’s collective bargaining agreement, players are docked 1/110th of their salaries for a missed game without a reasonable excuse. With Marbury scheduled to earn $20.1 million this season, that would be about $182,800.

Thomas brought Marbury back to his hometown in a trade with the Suns on January 5, 2004, and the two enjoyed a close relationship while Thomas was solely the team president. But things changed when he took on the job of coach as well before last season.

They clashed early last year after Thomas benched him in the second halves of two games, though they patched things up and Marbury played well the second half of the season.

But any problems on the court were minor compared to Marbury’s strange summer.

He behaved erratically during a televised interview, then testified in a sexual harassment trial against Thomas and Madison Square Garden that he had a sexual encounter in his truck with a team intern. Marbury was smiling and singing on his way out of the courthouse.

Marbury also was forced to apologize after defending Michael Vick’s participation in dogfighting.

The Knicks hoped their summer of woes would be forgotten once the season started, but instead they’ve blown up on their first road trip.

Marbury played poorly down the stretch in New York’s 75-72 home loss to Miami on Sunday, and the Daily News reported yesterday the Knicks were trying to reduce Marbury’s role or get rid of him entirely.

That created tensions between Marbury and Thomas — Westchester County neighbors who share the same agent. The two reportedly even fought on the plane to Phoenix, which the Knicks denied.

“There is no truth to that whatsoever,” a Knicks spokesman, Jonathan Supranowitz, said.

Marbury then left the team in Phoenix, telling the New York Post yesterday he had permission from Thomas. Thomas would not confirm that, but did say the team would welcome back Marbury.

Thomas refused to discuss any potential penalties against Marbury before the game yesterday, saying the matter would be kept “in-house.”

Several of Marbury’s teammates said his departure took them by surprise, but they expressed no hard feelings.

“You always support your teammates,” forward Jared Jeffries said last night. “A lot of people on the outside don’t understand what guys go through with their family, their friends, with this team, with anything. Whenever somebody goes through a tough time you support your teammate.”

Messages left for the agent, Jordan Bazant, were not immediately returned.