WASHINGTON — The airline industry’s dismal on-time performance extended through August with nearly 30% of flights delayed, according to government data that comes less than a week after President Bush promised to help fix the problem.

The nation’s 20 largest carriers reported an on-time arrival rate of 71.1% in August, down from 75.8% a year ago, the Department of Transportation’s Bureau of Transportation Statistics said today.

Through August, more than 25% of flights have arrived late — the industry’s worst on-time performance since comparable data began being collected in 1995. August’s on-time performance was the second worst on record for that month, topped only by a 70% arrival rate in 2000.

“Endless hours sitting in an airplane on a runway with no communication between a pilot and the airport is just not right,” Mr. Bush said last week.

Not all airlines suffered through poor performance in August. Aloha Airlines had the highest on-time arrival rate at 97%, followed by Hawaiian Holdings Inc.’s Hawaiian Airlines at 93.6% and Southwest Airlines at 77.7%, according to government data.

But almost half of Atlantic Southeast Airlines were delayed, and two of its flights arrived late every time they took off. The Delta Connection carrier, which is owned by SkyWest Inc., had the lowest on-time arrival rate at 55%, followed by United Airlines at 66.2% and Alaska Airlines at 67.1%.

Customer complaints nearly doubled in August to 1,634 compared with 864 in the same month last year, according to the government data. But the rates of mishandled baggage fell to about 7.6 reports per 1,000 passengers from 8.1 reports a year ago.