The First Interstate Bank advertisement says it's in Arizona. Hundreds of thousands of tourists believe it's in Arizona. And Arizona even claims it in its tourist literature.

But Monument Valley, which some say is the Southwest's most recognizable and marketable feature, is located, for the most part, clearly and undeniably in Utah."When you are selling a product, it doesn't do any good to say it is yours if someone believes it belongs to someone else," said Sue Halliday, a member of the Utah Travel Council.

And that someone else is Arizona.

In the cutthroat, billion-dollar business of Southwestern tourism, Monument Valley is a gold mine of economic opportunity, and Utah has yet to cash in. Grand Canyon tourists will travel north to see Monument Valley (believing they are in Arizona at the time), and will then backtrack to Arizona or detour to Colorado.

Only a paltry few venture farther north into Utah, state officials say.

"Of the thousands who detour to Monument Valley, most turn around and go back to Kayenta and then they are on their way to Mesa Verde or somewhere else," said Max Jensen, southeast regional manager of the state Division of Parks and Recreation. "They are not coming into Utah. They are not staying in motel rooms in Utah, or eating at Utah restaurants or spending money in Utah."

Which is one reason why state parks and the Utah Travel Council want to build a new Four Corners state park on state land on the Utah side of the Utah-Arizona border: to steer tourists to Utah's national parks and scenic wonders.

It would also give Utah a significant presence on a part of the Navajo Reservation where many of the Utah residents actually believe they live in Arizona.

Utah officials are yet uncertain what kind of state park should be built on the 20 acres of land (they hope to acquire 25 acres more). "Of course our interest is the visitor side of things," said Travel Council spokesman Joe Rutherford.

"If we had a visitor center there, we could display a lot of information about the state and hopefully convince a lot of people coming from the south that there are a lot more places to see and go to the north. We could use it to sell the rest of the state.

Parks officials, meanwhile, are looking at whether to build a museum, an outdoor market for Navajos to make and sell crafts, a picnic and rest area or perhaps all of the above.

Navajo officials from Monument Valley also want to incorporate the Navajo culture into whatever is done. Halliday says it is important to interpret the Four Corners area in light of the people who live there and their history.

"These are not the same Navajos who were herded up by Kit Carson and taken away," she said. "These are descended from the Navajos who escaped into the canyons and to Navajo Mountain and never were subjugated. They have a different heritage and history from those who live in Window Rock or Montezuma Creek."

The Monument Valley and neighboring Navajo Mountain Navajos also have a reputation as the most traditional Navajos anywhere on the massive reservation - a marketing aspect that could result in a one-of-a-kind state park.

Parks officials say park lands could be used by Navajos to weave rugs, paint sand paintings or manufacture jewelry while tourists watch. The Navajos could then benefit economically by selling their crafts in an open market atmosphere.

In addition to the Navajo culture, Jensen said, "We have all the movie history down here from the John Wayne days and we have all the geology. Yet there is nothing down here of any kind to interpret the Monument Valley area. Average tourists are quite disappointed once they get there."

The overall goal of building a new Four Corners state park is to offer tourists an interpretive experience once they get to Monument Valley and then offer them information on various destinations and loops in Utah.

The state, which has held the land for 25 years in hopes of building a state park, has appropriated $100,000 for planning the new facility, and state officials say they will approach the 1991 Legislature for actual construction funds.