Doctors today are curing 41 percent of all cancers, and in five years it will rise to more than 50 percent, the National Cancer Institute's new director said yesterday.

He credited this growing success rate -- it was only 34 percent 25 years ago -- to increasingly aggressive treatment, and in particular more sophisticated chemotherapy.

Appearing at his first new conference since he was appointed by President Carter Wednesday, Dr. Vincent DeVita Jr. cited the statistics and prospects for surviving various forms of cancer:

A long-term cure rate well over 50 percent for Hodgkin's disease, some lymph gland cancers and acute childhood leukemia, when found early and treated by specialists.

Five-year breast cancer survival improved from an average 63 percent in 1960-63 to 68 percent by the mid-'70s, with the figures now probably better, though not fully compiled. Five-year survival for localized breast cancer was 85 percent by the '70s, compared with 78 percent in the 1940s.

Five-year survival in colon cancer improved from 43 to 49 percent between the '60s and '70s; rectal cancer, from 38 to 45 percent; womb cancer, from 73 to 81 percent; bladder cancer, from 53 to 61 percent, and prostate cancer, from 50 to 63 percent.

In these cancers and others -- including hard-to-treat lung and stomach cancers -- "I think present treatments will show more real improvement," DeVita said.

By treatment success, he explained, he means not just a five-year cure rate -- though this is often used to measure progress -- but restoring a patient to normal life expectancy.

Today, he explained, "we can cure 41 percent of all patients with serious cancer." This includes all cancers except two kinds usually cured anyway: most skin cancer and localized cancer of the cervix (neck of the womb). With these included, the overall cure rate is 58 percent, but they are usually omitted to make the overall figures show the progress, or lack of it, being made in most cancers.

DeVita called the "exciting" prospect of more and more cures one payoff of an oft-criticized crusade against cancer ordered by Congress in 1972.

In the past few years, this stepped-up effort has been attacked by many critics, who say there are not enough cures despite the fact that the cancer institute budget has reached $1 billion a year. The critics include some of the members of Congress who voted for the effort, though many scientists warned them against expecting too much too soon.

The image of the program as a failure is "quite wrong," DeVita maintained.

Disagreeing in part with his predecessor, Dr. Arthur Upton, who said "a rosy view of the cancer problem is unwarranted," DeVita said, "I'm optimistic," but "you won't see the full impact" of new treatment until 1985.

In his first news conference since his promotion by Carter, he also said:

The cancer insititute is rapidly giving greater attention to cancer prevention. It is, however, almost wiping out a program to develop less hazardous cigarettes, though an American Cancer Society report said recently that they appreciably lessen damage to smokers' lungs.

"The most exciting" research prospect, one that may occur in the next 10 years, is "completely mapping" and understanding the molecule by molecule structure of human DNA, the body's genetic material.

DNA dictates all cell-making. Understanding how it works might lead to drugs to halt cancer's very development, not just drugs to make already cancerous cells stop multiplying. The latter is "what we do today," DeVita said.

But drug treatment has become far more aggressive and sophisticated, and in part this has been DeVita's doing. A 45-year-old, Bronx-born doctor, he joined the cancer institute in 1963.

In 1974 he became head of cancer treatment and in 1975 clinical director. Under him, the NCI developed the first effective combination drug treatment for Hodgkin's disease, a lymph-gland cancer that had been almost untreatable.

In the same years, in the same NIH clinical center or research hospital in which he treated cancers, DeVita's son Teddy was a gravely ill aplastic anemia patient from age 9 to age 17. The infection-prone youth died in May after eight years spent almost entirely in a five-foot-square plastic cubicle.

Throughout Teddy's confinement, DeVita remained an outgoing, cheerful cancer doctor, as well as his son's frequent chess-playing companion. He is widely regarded as a quick, decisive administrator, and his appointment is popular among NCI colleagues.

He said yesterday that he will also remain the institute's clinical director, or treatment chief. This means, he said, that he will spend 10 hours a week "making rounds" -- seeing patients and chewing over their treatment -- attending medical conferences and planning more research.