Millions of Americans should consider trying to drive their cholesterol levels lower than had been previously recommended, the government said yesterday, endorsing a more aggressive strategy for fighting heart disease, the nation's leading killer.

People at high risk for heart attack or stroke should explore with their doctor the option of taking higher doses of cholesterol-lowering drugs to cut their level of "bad" cholesterol below current targets, according to the National Cholesterol Education Program of the National Institutes of Health, which sets federal standards for preventing cardiovascular disease.

"The lower, the better, for high-risk people," said Scott M. Grundy of the University of Texas Southwestern Medical Center at Dallas, who chaired the panel that produced the guidelines. "That's the message."

By focusing attention on the benefits of reaching ultra-low cholesterol levels, the new guidelines are expected to intensify treatment of patients at the greatest risk and also push millions of others to begin treatment to lower their cholesterol, experts said.

"It's an important step forward," said Christie M. Ballantyne, a cardiologist at Baylor College of Medicine in Houston. "This affects millions of Americans and if implemented should lead to marked benefits by reducing heart attacks and strokes."

The move could mark the start of an eventual lowering of target cholesterol levels for all groups if research shows similar benefits for people at lower risk, experts said.

Evidence has been mounting that the lower cholesterol levels drop, the greater the benefit, and some doctors have begun treating cholesterol more aggressively. But this is the first time the government has validated the approach.

Heart disease is by far the nation's No. 1 cause of death, killing about 1.5 million Americans every year. High cholesterol increases the risk for heart attacks and strokes by accumulating inside arteries, narrowing passageways supplying blood to the heart and brain, and increasing the risk of a blood clot.

Because of growing evidence that lower cholesterol levels are healthier, the National Cholesterol Education Program convened the nine-member panel to review five major studies published since the last guidelines were issued in 2001.

In a paper published in today's issue of the journal Circulation, the panel created a new category of patients who should be considered at very high risk and recommended they consider lowering their levels of bad, or LDL (low-density lipoprotein), cholesterol to below 70. Previous guidelines said they should cut LDL to 100 or less.

People at very high risk are those who have heart disease, plus diabetes and high blood pressure, and smoke cigarettes, or also have "metabolic syndrome," a constellation of other risk factors, such as high levels of triglycerides, another fatty substance, and low levels of HDL (high-density lipoprotein), the "good" cholesterol.

The panel also recommended that people at moderately high risk consider trying to cut their LDL levels to at least 100, down from the now recommended 130. People in this group are those who have had a heart attack and have two or more risk factors that give them a 20 percent chance of having another one in the next 10 years.

The panel said anyone at high or moderately high risk should try to cut LDL levels by 30 to 40 percent.

Some experts criticized the government for presenting the new targets for high-risk patients as "options" rather than hard recommendations.

"As usual, the medical community is moving slower than the evidence and data support," said Eric Topol, chairman of the Cleveland Clinic's department of cardiovascular medicine.

The authors defended their decision, saying three large, ongoing trials should provide more definitive data within the next year or two, but they did not want to wait to give doctors some guidance.

"We have to be a little cautious about not being overly aggressive right now because we don't know how these trials are going to turn out," Grundy said. "We're going with what we've got, and that indicates that if you lower the levels to these very low levels that can be beneficial."

Other experts agreed, saying the step was prudent and still represented an important shift.

"I think it's a somewhat nuanced approach, but it's reasonable given the current situation," said Daniel J. Rader of the University of Pennsylvania School of Medicine. "It's a very big deal. It will increase the number of people who require more aggressive therapy dramatically."

The panel endorsed a combination of diet, exercise and cholesterol-lowering drugs to cut LDL levels. The most commonly used drugs, statins, are considered very safe but in rare cases can cause serious muscle and liver problems.

The panel left unchanged the recommendation that overall cholesterol levels should be below 200. Target LDL levels for lower-risk groups were also unaffected. But the guidelines endorsed the idea of cutting cholesterol in patients with diabetes and confirmed that lower cholesterol levels reduce risk even among the elderly.

Most heart disease researchers receive at least some funding from drug companies but maintain that their work is not influenced by such connections.