The cancer institute has spent $105 billion since President Richard M. Nixon declared war on the disease in 1971. The American Cancer Society, the largest private financer of cancer research, has spent about $3.4 billion on research grants since 1946.

Yet the fight against cancer is going slower than most had hoped, with only small changes in the death rate in the almost 40 years since it began.

One major impediment, scientists agree, is the grant system itself. It has become a sort of jobs program, a way to keep research laboratories going year after year with the understanding that the focus will be on small projects unlikely to take significant steps toward curing cancer.

“These grants are not silly, but they are only likely to produce incremental progress,” said Dr. Robert C. Young, chancellor at Fox Chase Cancer Center in Philadelphia and chairman of the Board of Scientific Advisors, an independent group that makes recommendations to the cancer institute.

The institute’s reviewers choose such projects because, with too little money to finance most proposals, they are timid about taking chances on ones that might not succeed. The problem, Dr. Young and others say, is that projects that could make a major difference in cancer prevention and treatment are all too often crowded out because they are too uncertain. In fact, it has become lore among cancer researchers that some game-changing discoveries involved projects deemed too unlikely to succeed and were therefore denied federal grants, forcing researchers to struggle mightily to continue.

About half of the scientists interviewed and/or surveyed reported that they now remove “red flag” words (for example, “AIDS” and “homosexual”) from the titles and abstracts of their grant applications. About one-fourth of the respondents no longer included controversial topics (for example, “abortion” and “emergency contraception”) in their research agendas, and four researchers had made major career changes as a result of the controversy. Finally, about 10% of respondents said that their experience had strengthened their commitment to see their research completed and its results published although even many of these scientists also engaged in some self-censorship.