Atlanta ? The racial gap in colon cancer death rates is widening, a new report says, and experts partly blame blacks’ lower screening rates and poor access to high-quality care.

Colon and rectal cancer death rates are now nearly 50 percent higher in blacks than in whites, according to American Cancer Society research being released today.

The gap has been growing since the mid-1970s, when colon cancer death rates for the two racial groups were nearly equal.

“We have seen this enormous progress in whites. We could be seeing the same progress in blacks, if we could overcome disparities in access to health care,” said Elizabeth Ward, who oversees surveillance and health policy at the cancer society.

Colorectal cancer is the third leading cancer killer in the United States. About 50,000 Americans will die of the disease this year, the cancer society estimates.

The rate of colon cancer diagnoses in blacks was about 19 percent higher than it was for whites in 2005, the most recent year for which statistics are available.

The death rate difference was even more pronounced. Among blacks, there were about 25 deaths per 100,000 people, compared with 17 per 100,000 in whites — a 48 percent difference.

Colon cancer deaths can be prevented by early diagnosis through screening and high-quality care. The screening rate for whites is 50 percent compared with just 40 percent for blacks.

The screening rate for Hispanics is an even-lower 32 percent, but the death rate for Hispanics — fewer than 13 per 100,000 — is lower than it is for whites.

That paradox is not unique to colon cancer: Poorly insured Hispanics have fared better than whites and blacks in several measures of cancer and heart disease.