WASHINGTON (AP) _ A slowing down in the decline of drug-related visits to hospital emergency rooms indicates drug use has nearly bottomed out at the ''bedrock'' addict level, the nation's drug policy chief says.

Statistics from the Drug Abuse Warning Network, or DAWN, released Tuesday by Health and Human Services Secretary Louis Sullivan show there were 426,060 drug-related visits to hospital emergency rooms in 1989 and 365,708 last year.

In the final quarter of 1989, the number of visits dropped from an average of 110,300 earlier in the year to 95,100.

Last year, the number dropped again in the second quarter to 91,800, then declined more slowly the next six months to a fourth-quarter total of about 88,100.

The number of drugs mentioned during emergency room visits - one patient often has taken more than one drug - decreased from 713,400 in 1989 to 625,300 last year, DAWN reported.

''We're getting close to the bedrock'' of the addicted, said President Bush's drug policy chief, Bob Martinez, pointing to the figures showing the decline in emergency room visits is no longer as steep as it was earlier. ''This is the most difficult population, the ones that perhaps have not listened to the messages.''

But an emergency room physician who has studied the DAWN statistics said the findings are misleading.

DAWN picks up only ''people who say they've overdosed,'' said Dr. Daniel Brookoff, an assistant professor of medicine at the University of Tennessee at Memphis.

Martinez conceded that DAWN may miss some drug cases because doctors diagnose a cocaine-induced heart attack victim only as a cardiac patient.

However, he said, the medical profession ''is statistic-oriented'' and aware of the need to keep track of drug abuse cases both for research and to support arguments for additional health facilities.

But Brookoff said it's often clerks who complete the paperwork based on sketchy information provided by doctors who don't know they should note a patient's drug use because they often aren't told their hospital is part of DAWN.

The situation with cocaine demonstrates the problem, he said.

DAWN showed a 28 percent drop in the number of cocaine mentions, from 109,700 in 1989 to 79,400 last year. Such mentions were close to the 30,000 level each quarter in 1989. Then they plunged to about 19,000 in the second quarter of last year and stayed there for the next half year.

''I am up to my eyeballs with this - people dying of cocaine, aborting babies on cocaine, going through all sorts of misery on cocaine,'' Brookoff said. ''The government saying this is on the decline is outrageous.''

A study by Brookoff at the University of Pennsylvania found that cocaine use was rampant among emergency room patients, although the hospital's DAWN reports didn't reflect that.

For example, Brookoff said, cocaine was used by 57 percent of the people who had been stabbed or shot, 20 percent of the women delivering babies and 30 percent of the people in auto accidents.

''None of those people got picked up by DAWN,'' he said.

The government argues that such people have never been included, so the trends still hold up.

But Brookoff said there are other problems of underreporting.

''Almost nobody diagnoses cocaine overdose anymore because we're more used to it,'' he said. Muscle shaking that was thought to indicate an overdose a decade ago is now considered merely the result of normal cocaine use and thus not recorded.

Meanwhile, experts have warned of a possible move toward heroin by those tired of cocaine's energizing effects and because of greater heroin supplies, and toward amphetamines - also known as speed, crank and ice - by those who want to ''buy American'' instead of from foreign cocaine suppliers.

But the DAWN survey indicates neither seems to be happening.

Heroin mentions during the two-year period peaked at 12,100 during the third quarter of 1989. The number dropped to 7,500 by the end of 1990.

As for amphetamines, there were 8,800 emergency room mentions in 1989, and 5,300 last year.

Marijuana mentions declined gradually during most of the two years, but then increased slightly at the end of 1990. Martinez said there was no indication why.