Sunday circulation of The Washington Post increased more than 2 percent in the past year to a record 845,176 for the six months ended March 31, while The Washington Star's Sunday circulation dropped almost 10 percent to 194,086, its lowest in more than 20 years.

Daily circulation of The Post increased 2.8 percent to 618,111, and the daily Star circulation fell 6.6 percent to 322,827, lowest since the Star merged with the Washington Daily News in 1972.

Circulation figures for the six-month period were reported to the Audit Bureau of Circulation by the two newspapers.

The ABC reports revealed the first year-to-year decline in the circulation of the Star since Time Inc. purchased the paper from financial Joe L. Allbritton.

Sunday circulation of The Star dropped below 300,000 for the first time since 1960 and was the lowest reported by the newspaper since 1957.

The Star has shown gains in both daily and Sunday circulation for each of the past two years and between 1979 and 1980 had recaptured a few thousand in circulation from The Post.

But the trend reversed dramatically in the past year, despite Time Incorporated's efforts to rejuvenate the Star, according to the ABC figures. The gap between the two papers' Sunday circulations increased by almost 50,000 as the Star's Sunday count fell by 32,426 and The Post gained 17,238.

With a Sunday lead over The Star of more than 550,000 papers, The Post captured 74.2 percent of the Sunday readership, to 25.8 percent for The Star.

The daily circulation of The Star was down 22,814 in contrast to a daily gain of 16.694 for The Post that widened the gap by more than 39,500 papers.

Now ahead by 295,000 papers a day, The Post's share of the daily newspaper circulation was 65.7 percent, compared with the Star's 34.3 percent.

Total Washington newspaper sales declined slightly last year because The Star lost circulation faster than The Post gained, the ABC data showed.