ATLANTA (AP) _ The live television audience for the first night of this year's Democratic National Convention was down significantly from 1984, figures from the A.C. Nielsen Co. showed Tuesday.

That continues the downward trend that began in 1980. The networks have experienced a general erosion in audience levels attributed largely to the proliferation of cable. CNN and C-SPAN are also carrying convention coverage.

NBC had a 6.2 rating and 11 share for its Monday night coverage, which began a half-hour earlier than the other two networks, at 8:30 p.m. EDT. CBS had a 5.8 and 11 and ABC a 5.7 and 10. All three major networks signed off shortly after 11 p.m. CNN had a 2.0 rating and a 3.3 share.

For the networks, the rating is a percentage of the nation's estimated 88.6 million households with televisions, and the share is a percentage of sets in use. For CNN, the rating is a percentage of households in the cable markets where CNN is available, roughly half of the total U.S. television homes. C- SPAN is not rated because it is does not run on advertising dollars.

In 1984, the Democratic convention had a rating of 8.4 on CBS, 7.7 on ABC and 7.1 on NBC. The 1980 convention rated a 9.6 on NBC, 9.5 on CBS and 8.0 on ABC.

The highest-rated Democratic convention since the events have been televised was the tumultuous 1968 convention in Chicago. It had a rating of 16.1 on NBC, 14.1 on CBS and 8.5 on ABC.