An ambitious proposal for a major expansion of the Salt Palace convention complex - including a new 25,000-seat arena for the Utah Jazz - offers exciting possibilities for the future of Salt Lake Valley.

The concept unveiled this week by city, county, and state convention and tourism officials would carry a price tag of at least $60 million. Included in the plan are:Construction of a 25,000-seat arena for basketball games, concerts, exhibitions, and large conventions. The Utah Jazz currently rank at the bottom of the NBA in home court seating capacity. Such a new arena would put the team near the top. It could be located west of the existing Salt Palace.

Expansion of existing Salt Palace convention and banquet facilities toward the south, taking over the parking terrace bordering 200 South.

Expansion of the Salt Palace Center exhibit space west along South Temple. Although the hall is large, it is much smaller than new facilities opening in Denver and San Diego.

Moving the Utah State Fair to this enlarged exhibit, entertainment, arena complex.

Swapping the Salt Lake Arts Center next to Symphony Hall with the Hansen Planetarium on State Street. The planetarium could then be expanded to become a science museum.

Construction of an outdoor Olympic-size speed skating oval.

Backers of the idea emphasize that none of this is finalized. The whole concept is offered as "possibilities." Yet in some respects, much of what is proposed can be classed as necessity. Salt Lake City already is losing large conventions because of the lack of facilities.

Two basic questions are raised by the concept. First, what happens to the existing Salt Palace arena if the Jazz play in a new facility, and second, who pays for this project?

County officials say the existing arena would continue to house the Golden Eagles hockey team, as well as concerts, conventions, and other shows. Apparently, the arena already is booked solid nine months of the year and some would-be users have to be turned down.

The financing would not cost taxpayers a cent, backers say. They see a combination of user fees, leases, private investment, land swaps and sales, Salt Lake Redevelopment Agency money, hotel-motel room taxes, and even Salt Palace income available when the Salt Palace bonds are paid off in 1995.

Clearly, the financing is crucial. Unless the funds can be raised - and rather quickly, since the Jazz would like to be in a new home by 1991 - the dream will come crashing down.

But given the impact the expanded complex can have on the valley and beyond, and the need for such facilities, every effort should be made to make the proposal a reality.

A task force of business and government leaders will begin meeting soon to work out details of the concept. That work should be pushed as rapidly as possible. This is a giant undertaking and delay will only add to the cost.