If Salt Lake City wants to move quickly in building a new Jazz arena, they might think again about building it in the southern downtown area after several Block 50 landowners threatened on Wednesday to tie up an expedited construction schedule in court.

The city Planning Commission voted 6-1 Tuesday in favor of the Block 50 site (site B) as a new home for the Jazz, rejecting a site northeast of the Salt Palace.But Block 50 business owners vowed to fight construction of an arena on their block, saying that the northern site proposed for the arena would displace fewer businesses and cost the city less in business relocation costs.

`If they want to get it started right away, we're going to tie it up as long as we can at this location," said Russell Sonntag, owner of Primrose Sonntag, a distributorship on Block 50.

"You bet your life," Sonntag said when asked if he would sue the city Redevelopment Agency, which will ultimately decide the arena's location, should it choose the southern site.

The RDA is expected to decide on Thursday where Jazz owner Larry Miller, who personally favors the northern Block 79 site, will locate his $45 million arena.

Jazz officials have said they would like the arena to be completed by the 1991-92 basketball season, and RDA officials have said they would like to complete land negotiations so that groundbreaking could begin in June.

The Planning Commission's decision angered some businesses and landowners on Block 50, who stand to have their properties condemned if the arena is located there. There are only two operating businesses on the northern site.

"No one is going to be hurt by locating at site A (the northern site), absolutely no one," businessman Richard Packer told the commission at a public hearing. "We are going to be hurt by site B."

The RDA could condemn and demolish properties belonging to unwilling sellers and has said businesses on the site chosen for the arena will have