By BRUCE HALLETT PRESIDENT

WHEN COLIN POWELL BOWED out of the 1996 presidential race last week, he showed just how swiftly the political landscape can be transformed. It is thus particularly fitting for TIME to introduce in this issue a new public-opinion survey that will enable us to provide the most accurate possible coverage of changes in voter attitudes during the 1996 campaign: the TIME/CNN Election Monitor. The year-long poll, drawn from a fixed sample of nearly 5,000 voters, will become a vital part of our reporting on both presidential and congressional battles. The sampling, says assistant managing editor Stephen Koepp, who oversees TIME's political polling, will yield what other polls have lacked: "Instead of just a snapshot, it'll give us a moving picture of voter opinion. We'll see the beginning, the middle and the end."

The Election Monitor poll, which will be conducted by Yankelovich Partners for TIME and CNN, is the largest and most rigorous of its kind. Traditional surveys sample the views of 1,000 or so randomly selected individuals who change with every questionnaire. The new format will permit us to track how the same voters' attitudes evolve, and will thereby enable us to pinpoint turning points in the campaign. Moreover, the sheer size of our sample will ensure that it corresponds closely to the views of the nation as a whole.

Within our large pool of respondents, we will also be able to zero in on narrowly defined demographic groups--Californians, for example, or senior citizens or religious and ethnic minorities. The categories can be as diverse as the country itself. "We will be able to measure every zig and zag of public opinion from any number of perspectives," says Hal Quinley, a Yankelovich partner and its director of political polling. "No one has tried anything this ambitious before."

For this week's issue, Quinley's team was able instantly to gauge the effect of Powell's decision by looking at whom his supporters listed as their second choice. As the political season unfolds, TIME will regularly combine results like this with sketches of the voters themselves. CNN has similar plans. Says Tom Hannon, the cable-network's political director: "We're going to use these surveys as the foundation for a lot of our reporting about how voters are responding to the campaign."

This sharing has been common since CNN joined the TIME-Yankelovich survey partnership in 1989. Neither partner, however, has ever had a tool for measuring the political mood of the country that is as powerful as the Election Monitor.