"I would express concern if we saw a big increase in claims, but we haven't," O'Reilly said. "We'll continue to monitor the situation."
The National Council on Compensation Insurance, a trade group whose members provide two-thirds of workers' compensation insurance to Maryland employers, also doesn't expect a major impact. Many of its insurers had already been compensating so-called Harris claims in all states where they offer policies.
But officials of the Injured Workers' Insurance Fund, a state-chartered insurer of last resort for businesses in Maryland, warned at a recent Senate Finance Committee hearing that hundreds of workers received some medical benefits but did not file a formal claim because they missed little work. They cost money but are not counted in the commission's statistics.
IWIF has paid $1.9 million to 600 workers who it says became eligible in the past six months.
"We felt Harris changed the law and we had to abide by it," said Thomas L. Bromwell, a former Baltimore County state senator who heads the fund. "The No. 1 concern for small businesses is not taxes, it's insurance. This will hit the industry. There is a cost."
Bromwell said the costs to IWIF, which insures about one-third of the market in Maryland, are expected to grow more than 7 percent from the Harris decision, contributing to a 3 percent premium increase this year.
It raised rates 11 percent last year before the Harris decision because of increased costs.
Some local governments, which often self-insure, also are worried about the new interpretation.
Baltimore County has reported 105 newly eligible cases, and Maryland counties overall are reporting an average of 5 percent more claims for the second half of last year than in the comparable period in 2002.
Suzanne Berger, an assistant Baltimore County attorney, called it "the tip of the iceberg." .
The Maryland Chamber of Commerce is supporting bills in the legislature that would limit eligibility for workers to pre-Harris standards.
It is also promoting legislation to create a panel of physicians to handle workers' compensation cases. The panel would have an "aggressive, more sports medicine-style approach to getting a person back to his job," said Heather D. Hamilton, a chamber vice president.
Robert E. McGarrah Jr., a senior policy analyst for the AFL-CIO in Washington, said employers should be responsible for those hurt on the job, as lawmakers intended in 1914.
"At this point, people are giving you estimates," said McGarrah, who urged a wait-and-see approach. "And you need uniform data. ... We're talking about injured workers."