In a nation that loves credit and, in fact, is hooked on it, an increase in interest rates immediately falls into the category of bad, even painful, news.

Couples postpone buying homes, cars, appliances and trips. Companies find their sales hurt. Lenders can't find qualified borrowers. Uncle Sam, always in a bind, finds it even more difficult to pay down his bills.Rising interest rates create a bad mood all around, because they signal - in fact, force - an economic slowdown. Few people look at whatever good higher interest rates might do, such as helping to avert inflation.

Among those least likely to see much good in the latest Federal Reserve action is George Bush, the Republican presidential candidate, because the VDI, or voter discomfort index, is now on the rise.

The VDI is a significant economic measure because it suggests discontent with the incumbent party. It has nothing to do with political fairness. It is not an in-depth measure of understanding, but it suggests how people vote.

As constructed by economist Albert H. Cox Jr., the VDI is made up of the jobless rate, mortgage rates, inflation rate and growth rate. The first three are added, and the fourth is then subtracted from the total.

In 1976, the year of President Carter's election, the VDI was 16.1, made up of a 7.7 percent jobless rate, 9 percent mortgage rates, 4.8 percent inflation rate and 5.4 percent growth rate, the latter based on gross national product.

It was a high rate and rising - it was only 10.9 in 1976 and as low as 7 in 1964 - which helped defeat the incumbent.

By 1980 it was even higher, and rising. In fact, it had doubled to 32.5. The job situation had improved a bit, but mortgage rates and inflation were in double-digit areas, while economic growth had almost ceased. The mood was blue.

As everyone knows, Ronald Reagan rode into the White House on a surge of votes, a consequence at least in part of the terrible VDI. By 1984 the VDI was back down to 17.4, and Reagan was re-elected in a landslide.

The current VDI is just under 16, which means it has shown very little improvement since 1984. The unemployment and mortgage situations are better. Inflation is about the same. But economic growth has been cut in half.

In other words, says Cox, senior economic adviser of Bil, Trainer Wortham Inc., favorable economic momentum is not evident if the reference point is economic conditions before the last national election.

And now that the Federal Reserve has raised its basic interest rate to 6.5 percent from 6 percent, the VDI may very well deteriorate. While inflation still could worsen, economic growth might slow.

Cox observes that "President Reagan made effective use of the question: Are you better or worse off? Obviously, the answer to that question was `much worse off' in 1980, and `much better off' in 1984."

What would the answer be today? "Neither, or not sure or don't know," said Cox when he compiled his latest VDI. But that was before the Fed raised interest rates. Today, the interpretation would be even worse for Bush.

The VDI doesn't tell it all. It is a record of existing conditions and says nothing whatever about the ability of a candidate to inspire voters and to portray a new and better economic life. But it sets the mood.

Says Cox: "Economic momentum, both negative and positive, was a powerful factor in President Reagan's big election victories. If he were running again this year, he would not have that advantage. . . . and candidate Bush does not have that advantage."