First, the bad news: Americans have a third less leisure time than they did a decade ago, according to a survey on "Americans and the Arts" released here today by pollster Lou Harris. Eight hours a week of free time have vanished. Women have the least amount of leisure time.

Now the good news: Somehow people have managed to spend more time seeing movies, plays, concerts, dance performances and art exhibitions. Last year, in fact, the number of Americans attending arts events topped the number attending sports events, participating in political elections or traveling.

More than 70 percent of those polled said they would vote to increase taxes to benefit the arts. The same number, said Harris, would cast votes to decrease taxes allocated to defense spending.

"When you get numbers like this," he said, "you have to admit that the arts are mass, mass, mass. And when you get people saying that they would pay more taxes, well, you know it's time to take this seriously."

The findings were based on a survey conducted by telephone -- in this case, a sample group of 1,504 adult Americans polled in March 1984. The results of the survey, the fourth such poll on Americans and the Arts since 1973, will be presented at a Congressional Caucus for the Arts in May.

Harris would not release figures on attendance at sports events -- he will reveal those next week -- but he did say they would prove that sports attendance is down.

Despite the drop in available leisure time, a record number of Americans found time for the following:

* 134 million went to the movies, up 8 percent over 1975;

* 115 million attended a live performance of a play, musical comedy, pantomime or other theater event in 1984, an increase of 14 percent over the past decade;

* 103 million watched live pop concerts, including rock concerts and performances by popular singers or bands, an increase of 14 percent over the past decade;

* 58 million attended classical music performances, including opera and symphony, in the past year, up 9 percent over 1975;

* 58 million saw live performances of dance, including ballet, modern, folk or ethnic, an increase of 11 percent over the past decade.

The numbers dropped in only one category: attendance at art museums. Last year 100 million Americans attended art museums, a decrease of 2 percent over the 1980 figures.

"Art museums attendance has plateaued," said Harris.

This year, for the first time, arts programming on television was included in the poll. Forty-seven percent of the households surveyed subscribe to cable; 17 percent own VCR units. But among those with access to cultural programming, 90 percent said that "to see something performed live on stage is more meaningful and exciting than watching it on TV," up from 81 percent in 1975.

When asked why he thought the arts continue to capture the leisure time of many Americans, Harris responded, "People may feel good about the Olympics and patriotism, but by and large we have had a rough decade. People are working more. Stress is up. The arts provide a positive release from this. People say they are uplifted by an arts event. They feel improved and relaxed by the experience.

"The people have spoken," he said. "I think we may see a change in priorities. Already in the private sector I have seen this change coming. Monday night football is down. Dining out is down. Race-track attendance is down. But the arts are up. Where do you put your money?"