Tom Warner was attending a Washington Board of Trade seminar in 1985 when he got a clue as to why his company had trouble keeping young employees.

The president of Warner Corp., a Northeast Washington plumbing business with about 220 employees, said the firm had been losing about 75 percent of its apprentices to various problems. When he heard the seminar speaker describe the effects of drugs on workers and the workplace, saying that 20 percent of the working population uses them, "it made clear that so many of our problems were drug-related," he said.

Since the family-owned company was spending about $4,000 per person to train the 20 apprentices it hired each year, pinpointing the source of the problem was crucial.

Many employees failed the drug testing he instituted, at times depleting the staff to the point of idling as many as 25 trucks. Eventually, he said, through referrals from his employees and by advertising his company as a drug-free workplace, he solved the labor shortage. The firm's productivity rose and accident rates fell, especially "bizarre situations" such as accidents in customers' homes, he said. Business also increased as a result.

Warner started hiring consultants to talk to managers about detecting on-the-job drug use, but testing was the key, he said. Although the drug testing costs at least $7,500 a year, he said, it saves $2,000 a year per employee in insurance and training costs.

"Once we started screening, it was like night and day," Warner said. "Everybody stayed -- it was a dramatic change in the company."

The drug abuse seminar Warner attended and the program that followed it are two ways in which businesses small and large are trying to deal with the problem. A 1987 Conrail crash helped draw national attention to drug abuse on the job, prompting a spate of corporate drug testing programs and a new federal law that, among other things, says that companies without a clearly stated anti-drug policy can't do business with the federal government.

On-the-job accidents are only one aspect of the problem. Authorities say that drug- and alcohol-abuse problems also are linked to family troubles and job stress.

For many companies, however, the steps Warner took are not the most effective.

Another approach is being taken by the Corporation Against Drug Abuse, a nonprofit organization of local executives founded in 1988 to collect information about prevention and treatment programs for drug abuse in the workplace.

The organization received a Labor Department contract to develop a series of workshops, the first of which was held last week, to help companies set up policies to comply with the new federal law. The sessions also are intended to give executives of small firms an introduction to employee-assistance programs that provide education and referral help for workers with personal problems.

Irene B. Ansher, a consultant with Vienna-based QASystems Inc., designs and evaluates employee assistance programs. The Corporation Against Drug Abuse hired Ansher to set up the seminars for small and medium-size companies that could not afford to set up such programs.

Drug problems slow a company's productivity and involve more people than just the drug user, she said. "In a small company, a manager or an owner may spend a lot of time trying to fix something himself," Ansher said, and the supervisor will "cover up {the problem} and do the work for that person."

While such programs may be most important to small companies where each employee's performance is crucial, they are the ones least able to afford them. Ansher said many employee-assistance providers don't want to draw up programs for small companies for base fees of less than $5,000 a year.

The corporation is seeking ways around the price problem by setting up consortiums of companies with a shared policy. Other small businesses take a different tack, contracting social workers to educate employees and supervisors and be on-call to provide limited counseling.

"When you listen to these small businesses, you often hear the top people don't want to spend the money on it," Ansher said. She said she often hears: " 'Why should we spend the money on it if we don't have a problem?' "