Hardly a Utahn is now alive who can remember when projects to tap the state's share of the Colorado River were not under discussion, deliberation, or construction.

It is probably incomprehensible that actual work on the Central Utah Water Project is within half a dozen years of completion, or that so close, it could be cut off by Congress.Utah and the other Colorado River states divided the river up in the 1920's at a time when the Colorado's flow was higher than it was to be again for more than half a century. The dry years did not really matter. After Hoover and Parker dams were built, California stalled upstream states from tapping the river for their shares.

The Upper Basin states won their fight in 1956 with passage of a law allowing Flaming Gorge and Glen Canyon dams and a raft of participating projects to be built. The California-Arizona battle was not resolved until the 1960's, clearing the way for the Central Arizona Project. Then-Colorado Congressman Wayne Aspinall pushed through additional - if shaky - projects in his state.

But if Congress does not increase the cost ceiling of the Colorado River Storage Project, the entire Upper Basin Project will grind to a halt well short of completion of its main water delivery projects.

On Utah's Bonneville project, $797 million will have been spent by Oct. 1. Another $143 million is on its way through the congressional pipeline for the fiscal year that ends Sept. 30, 1989. If everything projected for CUP were built, another $750 million would be needed.

No one now believes that all of that will ever be built. Utah's members of Congress have all but abandoned the Upalco project and some smaller, but costly, features. The Unitah project, and means to provide water promised to the Ute Indians, will probably be dealt with outside the Upper Basin law.

While projects to provide water to farmers have been cut back, some $200 million in work to provide water to fish and wildlife have been added. On balance about another $400 to $500 million would finish the work.

Congress seems not disposed to provide the money.

Irrigation of possibly surplus crops is out of favor in Washington. Environmentalists oppose it, the size of the deficit makes it a lower priority than it once was, and public power users shy away from paying for it by power sales from the big Colorado dams.

The latter approach is the one sought by the Utah congressional delegation and, in fact, the method envisioned by Congress years ago to finance water projects.

What would happen if Congress just refused to lift the ceiling? When would the bulldozers clank onto contractors' trailers and be towed away, the vast borers cease augering the water tunnels, and the Bureau of Reclamation engineers pack up their clipboards and leave?

Regional Reclamation Director Cliff Barrett says The Jordanelle Dam and Syar Tunnel would be the last major contracts he could award.

Design work on the two Diamond Fork tunnels would be slowed, or abandoned if Congress gave a clear signal it was going to cut off the project. They would not be built.

None of the planned irrigation works - the Wasatch Aqueduct and the Loafer Mountain Tunnel - would go to construction. Design on them is already being slowed in anticipation that the Central Utah Water Conservancy District will build them, not the Bureau.

The Wasatch Front, now receiving 20,000 acre feet of water from the project, might get another 74,000 acre feet - the designed amount, if some relatively minor works were built.

Another 180,000 acre feet assigned to irrigation could be shifted to municipal use, depending on demand and price. Alternatively that water might be left in the Unita Basin, or allowed to flow back into the Colorado River.

Some minor amount might go for irrigation using existing systems for delivery.

The cost of water in Salt Lake Valley would rise from its current $200 per acre foot price for Bonneville water to $350, $400 or much, much more, if all of the project costs were placed on water users.

Probably the valley would eventually use all of the potential 270,000 acre feet of water as the population grows. That would amortize the cost to a somewhat lower figure than under the worst-case scenarios.

The $200 million in wildlife project work would not be built, leaving some streams dry and others with more water than otherwise.

The last big loser would be Uncle Sam. If CUP was never completed the federal government would not have fulfilled its contract and, Sen. Jake Garn vows, would never get a penny of repayment for the $940 million the taxpayers have invested.