WASHINGTON — If Congress doesn’t get the job done, Education Secretary Margaret Spellings says she’ll consider using her authority to require states to report high school graduation rates in a more uniform and accurate way.

“I think we need some truth in advertising,” Spellings said, referring to the hodgepodge of ways states now report graduation data.

States calculate their graduation rates using all sorts of methods, many of which, critics say, are based on unreliable information about school dropouts.

Republicans and Democrats in Congress have drafted proposals to better gauge how well high schools are doing at getting students diplomas, and doing it on time. The changes are part of a rewrite of the No Child Left Behind education law, but that bill’s progress has stalled amid disputes over unrelated testing and teacher pay issues.

Spellings said if that standoff persists, her department has the power to address the reporting of graduation rates. “I think it can be done through regulations,” she said.

The most common methods used by states to calculate graduation rates assume there’s good data on the number of dropouts, something that generally doesn’t exist. A student who stops coming to school, for example, often is assumed to have moved and gets counted as a transfer, when in fact the student may have quit school.

“If you use dropout data, you need to be very concerned,” said Chris Swanson, director of the Editorial Projects in Education Research Center, which has published studies on the issue.

Under No Child Left Behind, states may use their own methods of calculating graduation rates and set their own goals for improving them. Critics say that’s a loophole.

Some states, for example, give themselves passing grades as long as they make any progress at all on graduation rates from year to year.

States’ methods of counting graduates also are flawed and lead to overestimates, according to reports by both the Education Trust, which advocates for poor and minority children, and the Alliance for Excellent Education, another group focused on the issue.

Using federal data, researchers such as Swanson generally estimate the nation’s on-time graduation rate at about 70 percent. For minorities, they say it drops closer to 50 percent.

Washington state reported a graduation rate of 79.3 percent in 2005, while the federal estimate for the state that year was 75 percent.

The Education Department uses a formula for estimating the graduation rate of each state by comparing diplomas given out against the enrollment figures for that class in earlier grades. In nearly all cases, the federal estimate is lower than the state-reported rate.