The House Energy and Commerce Committee plans to ask Congress’ investigative arm to study the television ratings system used by Nielsen Media Research to determine whether it accurately calculates the number of Americans watching certain television shows.

The request, which is expected to come formally next week in a letter to the General Accounting Office, is a major setback to Nielsen’s efforts to roll out a new electronic ratings system that it says more accurately calculates the ratings that determine how much the television industry can charge for ads.

The request could effectively delay the company’s new Local People Meter system by six months or longer, because it asks Nielsen to continue using its current paper recording method until the GAO concludes its study.

A similar GAO study on new packages for cable programming took about nine months. Other GAO studies have lasted well over a year.

“We fully intend to ask Nielsen to continue using both the diaries and the Local People Meters until the GAO finishes its study,” said John Tripp, a spokesman for the Energy and Commerce Committee.

The letter hands an important victory to minority groups and to News Corp., which owns the Fox broadcasting network. They charged that the new Nielsen system undercounts black and Hispanic viewers.

Nielsen had hoped to roll out the new system in New York City last month. But a political firestorm in New York and Washington forced the television ratings company to delay until June.

Nielsen wants to launch the Local People Meters in Los Angeles and Chicago in the next few weeks.