A share point represents the percentage of homes using television at the time that are watching the program.

In New York, a ratings point represents about 70,200 homes using television.

Each rating point represents 931,000 homes using television.

S. is to increase prime-time ratings and the shares there because there are more homes using television at that time.

According to Nielsen, the number of homes using television has decreased more than 4 percent since mid-January.

"There are more homes using television at 7 than there are earlier," Mr. Moll said.

These are research terms that stand for "Homes Using Television" and "People Using Television."

David F. Poltrack, the senior vice president of research for CBS, said viewing levels - also known as HUTS, for "homes using television" - have been acceptably accurate this fall.

Although that would not account for the drop in levels of homes using television, it would help account for the even bigger - and more costly - declines being recorded in the number of viewers, he said.

The latest falloff in what Nielsen calls "homes using television" for the prime-time hours in February was the fourth decline in five years (the figure increased in February 1994 during the Winter Olympics).

In New York and Washington, where temperatures reached 100 degrees last week, the so-called HUT levels (which stands for homes using television) showed no real changes in television viewing beginning on Wednesday when the temperatures first soared, according to Nielsen, which compiles the data daily.

The share is the percent of households using televisions that are tuned to the program.

"This will give us the ability to let more people watch the games later in the day, when the number of households using television are higher.

"The households using television drops off so dramatically as you approach July 4 weekend that I don't think that's a realistic possibility," he said.

The viewer-tuneout trend has been detectable since about mid-January, Mr. Jacoby said, with the so-called H.U.T. levels (for households using television) falling off each month since.

In their efforts to increase ratings, the networks have conducted their own research and concluded that by concentrating only on households using televisions, Nielsen fails to measure many viewers, like those in hotels, dormitories and bars.

All helped give basic cable its best week ever in the Nielsen ratings, with an average prime-time share of 47, meaning of all American households using television last week, an average of 47 percent were tuned to a basic cable channel in prime time.