Both boards of directors for PacifiCorp and Utah Power & Light Co. acted swiftly this week to approve their $2 billion merger in the wake of last week's green light from a federal agency. But one more significant obstacle still lies in the path of that long-awaited union.

The Utah Public Service Commission earlier was one of the seven state regulatory agencies to approve the merger. But now it wants to re-examine the proposal as it affects Utah consumers.Why the backing away at this late date? The reason is simple. The PSC wants to make sure that the results of the merger, and the earlier promises attached to it, are still able to be carried out.

When the Federal Energy Regulatory Commission approved the merger last week, it did so only under certain conditions. The FERC required the merged company to open its electric power transmission lines to other utilities.

This sharing could affect the profitability of the new entity - and thus the utility rates for Utahns. Both companies had pledged earlier that the merger would provide at least a 5 percent cut in UP&L rates.

The PSC understandably is concerned that the merger have a beneficial impact on Utahns. That was one of the major reasons for giving the go-ahead earlier. The word is that commissioners are going to be tough on this issue.

If the utilities are unable to keep their pledge of rate cuts because of federally-imposed conditions, the merger makes less sense for Utahns.

There are other reasons, of course, for the joining of the two utility companies. The merger calls for UP&L to become a division of PacifiCorp, which already owns Pacific Power & Light Co. The new entity would be one of the bigger utilities in the nation, serving more than 1 million customers in seven Western states. This certainly would strengthen UP&L.

The best result to be hoped for is that UP&L could offer lower rates -despite the conditions imposed by the FERC - because of savings gained by greater efficiency, sharing of power, lower construction costs, and lower labor costs.

The PSC is required to watch out for the interests of consumers as well as the utilities. In this case, the merger must benefit both, not just one side of the equation.

The swift approval by the boards of directors would seem to indicate that both companies think they can live up to their earlier promises.