WASHINGTON (AP) _ Government scientists have begun a three-year effort to measure the sediment and chemicals in the Mississippi River.

The water quality of the nation's biggest river is being measured through samples taken by U.S. Geological Survey scientists traveling along it.

The team began work at Hermann, Mo., and will finish the first leg of the effort Saturday just south of New Orleans, the survey reported.

''By developing an understanding of how a large river system such as the Mississippi moves, mixes and stores sediment-related contaminants, we can provide information useful to state and local agencies that are responsible for dealing with the detrimental effects of these contaminants,' ' said survey hydrologist Robert Meade of Denver, coordinator for the study.

There will be a second collection effort in December, and the sampling will be repeated periodically over three years.

The water samples will be tested for sediment and various chemicals to learn how these materials behave in the water and how they are transported downstream or deposited along the way.

Repeating the measurements about every four months will allow the scientists to develop an understanding of seasonal and long-term variations in the river, Meade said.