Race and place of residence can have a staggering impact on the course and quality of the medical treatment a patient receives, according to new research showing that blacks with diabetes or vascular disease are nearly five times more likely than whites to have a leg amputated and that women in Mississippi are far less likely to have mammograms than those in Maine.

    The study, by researchers at Dartmouth, examined Medicare claims for evidence of racial and geographic disparities and found that on a variety of quality indices, blacks typically were less likely to receive recommended care than whites within a given region. But the most striking disparities were found from place to place.

    For instance, the widest racial gaps in mammogram rates within a state were in California and Illinois, with a difference of 12 percentage points between the white rate and the black rate. But the country's lowest rate for blacks - 48 percent in California - was 24 percentage points below the highest rate - 72 percent in Massachusetts. The statistics were for women ages 65 to 69 who received screening in 2004 or 2005.

    In all but two states, black diabetics were less likely than whites to receive annual hemoglobin testing. But blacks in Colorado (66 percent) were far less likely to be screened than those in Massachusetts (88 percent).

    The study was commissioned by the nation's largest health-related philanthropy, the Robert Wood Johnson Foundation, which on Thursday planned to announce a three-year, $300 million initiative intended to narrow health care disparities across lines of race and geography. Officials said it would be the largest effort to improve health care quality ever undertaken by a charity in the United States.

    The foundation hopes to better understand and confront the causes of those regional variations by focusing its spending on 14 regions, like the city of Memphis and the state of Wisconsin.

    Dr. Bruce Siegel, the George Washington University professor who will direct the program, said one community might use its grant money to study how long it takes hospitals to move heart attack patients from emergency room to catheterization laboratory. Others might work to coordinate electronic record-keeping or to provide patients with better information about taking medications after discharge.

    "In my book," Dr. Siegel said, "health care is local, just like politics, so you're going to see a lot of differences in what communities do."

    That point is reinforced time and again in the new research conducted by the Dartmouth Atlas Project of the college's Institute for Health Policy and Clinical Practice, which has used Medicare data to document health care disparities over the last two decades. It found substantial variation in the proportion of Medicare beneficiaries who had been seen in a two-year period by a primary care physician, ranging from 86 percent in Nebraska and South Dakota to 65 percent in New Jersey. It found far higher rates of unnecessary hospitalizations in Hawaii, Utah and Washington than in Kentucky, Louisiana and West Virginia.

    Disparities in the rate of leg amputations were particularly stark. The rate for blacks was about 6 per 1,000 in Louisiana, Mississippi and South Carolina, but less than 2 per 1,000 in Colorado and Nevada. The rates for whites in the three Southern states were much lower, about 1.3 per 1,000, but were still more than double the rates for whites in the two Western states.

    Such variations may be partly explained by regional differences in education and poverty levels, but researchers increasingly believe that variations in medical practice and spending also are factors.

    "In U.S. health care, it's not only who you are that matters; it's also where you live," wrote the study's authors, led by Dr. Elliott S. Fisher.

    Dr. John R. Lumpkin, senior vice president of the foundation, said that more than a third of the $300 million would be spent to hire national experts to help regional coalitions tailor their quality improvement plans. The remainder of the money will be devoted to research, evaluation and the promotion of quality standards.

    "We want to build a template in each of these communities that will teach America how to improve health care quality in a dramatic way," Dr. Lumpkin said.

    The areas selected for the grants are Cincinnati; Cleveland; Detroit; Humboldt County, Calif.; Kansas City, Mo.; Maine; Memphis; Minnesota; Seattle; south central Pennsylvania; western Michigan; western New York; Willamette Valley in Oregon; and Wisconsin.

    The foundation's endowment, now about $10 billion, was financed originally from the wealth of its namesake, who died in 1968 after building Johnson & Johnson into one of the world's largest sellers of health and medical products. The group has been a major force in curbing tobacco use, and has more recently turned its attention to obesity, announcing a five-year, $500 million effort on that front last year.