WASHINGTON — The Internal Revenue Service is not living up to its pledge to crack down on wealthy tax cheats, an IRS watchdog group says, citing a drop in audits of millionaires last year. The tax agency disputes the conclusion, ascribing the "slight" decline in audits to its focus on getting people their economic stimulus checks. Those with incomes of $1 million and above had a 5.6 percent chance of getting audited in fiscal year 2008, which ended last September, down from 6.8 percent the previous year, according to IRS figures.