Indexation of taxes, the inflation-fighting scheme that is so controversial on Capitol Hill, is catching on rapidly at the state level, two University of Virginia researchers report. Of 44 states with personal income taxes, nine have already adopted some form of indexing, and six more, including Virginia, are considering it, according to John L. Knapp and Philip J. Grossman. The reason, they say, is inflation and the impact it has had on the tax burden. "Income tax systems," they write, "developed when prices were fairly stable, have been characterized by unlegislated increases in effective rates . . . In 1979, a year of double-digit inflation, 95 percent of the increase in state tax collections resulted from inflation." And "with forecasts of continued high rates of inflation, it can reasonably be expected that the indexing movement will grow." The impetus comes from the fact that most tax systems are "progressive," so that when a taxpayer's income rises so does his tax liability. But if the income increase is due to solely inflation, the taxpayer can find himself with no gain or even a loss in buying power. Indexing is already on the books in some form in Arizona, California, Colorado, Iowa, Minnesota, Montana, Oregon, South Carolina, and Wisconsin. In most of these states, the two researchers found, inflation adjustments are made in the "three primary fixed-dollar features of the personal income tax" -- income brackets, personal exemptions and maximum standard deductions. "As would be expected, indexing resulted in a reduction in the rate of growth of tax revenues," write Knapp and Grossman, who are with the Tayloe Murphy Institute, a research arm of the university's business school. Some states have used surpluses to cover these losses, but most of the officials that Knapp and Grossman surveyed said that in the long run they expect there will be spending cuts.