As the House prepares to vote next week on how hard to crack down on the nation's HMOs, lawmakers are splintered over proposals that would give Americans who are angry with their health plans the ability to sue them.

While partisans on both sides of the debate have offered shrill predictions of what would happen if Congress adopts such a law, only one state provides a glimmer of actual evidence. Two years ago, Texas became the first state to eliminate a legal quirk that has largely stifled such lawsuits, and the experience there so far suggests that the ripple effects could be fairly gentle.

The insurance industry and its business allies have spent millions of dollars warning legislators in Washington that it would be dangerous to give patients the right to sue health maintenance organizations, arguing that the courts would be deluged with baseless litigation and health care would become unaffordable.

But since the Texas legislature made managed-care plans liable for malpractice, there have been only five known lawsuits -- the most recent just this month -- from among the 4 million Texans who belong to HMOs.

And despite insurers' arguments that such a law would force them to practice an expensive brand of defensive medicine, there is no sign that medical costs are rising faster in Texas than elsewhere in the country.

"The sky didn't fall," said state Sen. David Sibley, a Republican who was the law's main champion in the Texas legislature. "Those horror stories" raised by the industry "just did not transpire."

However, the state's insurance and business groups say that the law's full effect has not had time to materialize, noting that the first suits remain in the early stages and that the law itself is being challenged in federal court. "I wince when I hear, `There is no effect in Texas,' " said Jeff Kloster, general counsel of the state's HMO trade group, the Texas Association of Health Plans. "It ain't here yet. It's coming."

Which view of the Texas experience is correct has widespread relevance as "patients' rights" has become a hot issue, plunging Congress and state legislatures around the country into fierce debates over how far to tip the balance of power between patients and the managed-care plans that dominate the nation's health care system. Georgia and California have just given consumers the ability to sue HMOs.

The U.S. Senate passed a Republican "patients' rights" bill this summer that would not allow people to sue. But in the House, the GOP is so divided that it is far from clear which of three HMO bills will prevail when the issue comes to the floor next week.

Most House Republican leaders, sympathetic to the insurance industry, oppose the idea of permitting lawsuits. But a relatively small but potent group of party rebels have sided with consumers, doctors and Democrats, who insist that patients need the right to sue to deter managed-care plans from denying the care they deserve.

In the statehouse in Austin, the issue pitted insurers and business groups in a furious lobbying battle against doctors and lawyers, but it had a markedly less partisan cast than the fight on Capitol Hill. The idea emerged from five conservative legislators -- three Republican, two Democratic. Sibley, the bill's main sponsor, is a lawyer, a former doctor and an ally of Gov. George W. Bush (R).

In the winter of 1997, when Sibley began a series of meetings in his conservative Waco district to explain why he favored the idea, he worried about how people would react. At the first get-together with a local Republican group, he was stunned by what happened. "I got a standing ovation," he recalled.

Public antipathy toward HMOs, it turned out, was stoked the very week the legislation was introduced. The largest HMO in Austin announced it would eliminate coverage for all but one kind of allergy medicine -- and would limit patients who wanted that kind to one pill a day. The state's insurance commissioner drove to the office of PCA Health Plans of Texas to protest, and the HMO backed off.

That spring, the bill passed with overwhelming support from both political parties. Bush, now a Republican presidential candidate, had opposed the idea of allowing HMOs to be sued and had vetoed a similar measure two years earlier. But this time, in a position that puts him at odds with GOP leaders in Congress, he let the law take effect without his signature.

Two years later, a Bush spokesman said the governor believes the law has "worked well," primarily because of a grievance system included in the legislation that has ruled on about 600 cases and sided with patients about half the time. "We have not seen an explosion of lawsuits," said the spokesman, Ray Sullivan. "That's what the governor wanted."

Health care officials, politicians and policy experts disagree over why the Texas law's effects have not been more pronounced so far.

Some say that the grievance system that Texas set up two years ago for patients who believe they have been cheated of proper care -- a feature of all the "patients' rights" bills before Congress -- is working, resolving people's complaints before they land in court.

Health plan administrators and physicians across Texas say they have an intuitive sense that the threat of lawsuits has made HMOs more lenient. Joe Cunningham, an internist in Waco, had asked an HMO a year ago to allow a patient to undergo an overnight study to find out if he had sleep apnea. At first, an HMO official balked, but when Cunningham said he worked in Texas, he said he was told, "Oh, well, okay, do the test."

But most of the state's HMOs are not keeping track of whether they are, in fact, permitting more care. Asked to identify health plans in Texas that have been forced by the new law to raise prices or to give patients expensive medical services they don't really need, the state's HMO trade group, the American Association of Health Plans and the Health Insurance Association of America each surveyed their members and said they could not find an example.

One of the few HMOs to complain publicly has been Scott & White, a small nonprofit health plan in central Texas, which last year wrote a letter to its congressional representatives -- widely circulated by industry advocates in Washington -- saying that its premiums were going up by 15 percent and that it was approving all requests for care "with rare exception." But Deny Radefeld, the plan's executive director until last month, said the premium hike was caused partly by other factors, including the soaring price of prescription drugs.

Cost information that HMOs must file with the Texas Department of Insurance shows that, since the law took effect, there have been no unusual increases in the amount that plans spend on medical and hospital services. In fact, the data show that HMOs operating in both Texas and other states tend to have bigger cost increases elsewhere in the country.

HMO officials contend that premiums in the state will go up eventually, once major settlements or jury awards are won. Some also say the consequences of the Texas law may not foreshadow what would happen elsewhere because it permits somewhat fewer suits and smaller awards than some bills in the House.

Plaintiffs' attorneys in Texas acknowledge that they are proceeding gingerly for now, choosing their first cases with special care to try to make the point that some HMOs stint on care.

In three of those cases, patients allege they were unable to get cancers diagnosed for months because their health plans denied them tests or visits to oncologists. One patient alleges that he needlessly was left disabled by a stroke because an HMO delayed his treatment by requiring him to transfer to a different hospital. Another suit was filed by the family of a suicidal man, ordered home from the hospital against his psychiatrist's advice, who went into his garage that night and drank a lethal half-gallon of antifreeze.

"Life is very cheap to [HMOs], it seems," said Rosemary Dudley, 66, of Fort Worth, who sued her health plan in April, contending that the cancer that had first appeared in her breast was able to spread unchecked to her lung and jaw for eight months because her family doctor had stopped letting her see an oncologist. "I think maybe [the law will] put a hold on them doing things like this," said Dudley.

The health plans that have been sued refused to comment because the cases are in litigation.

So far, the Texas law seems to have made little impression on the debate in Congress. Rep. Gene Green (D-Tex.) often invokes his state's experience, saying it implies that "all the fear factor we're hearing is just exaggerated." But key Republicans have embraced the insurance industry's point of view. Said Rep. John A. Boehner (R-Ohio): "It's very premature to make predictions based on what is happening in Texas."