President Reagan said yesterday that a growth removed from his nose last week turned out to be "the most common and the least dangerous" kind of skin cancer, caused by over-exposure to the sun, and that no further treatment was needed.

In answer to a question at a news conference in the Oval Office yesterday, Reagan said that what he called a "pimple on my nose" had been "snipped off" last Tuesday, but that he had learned over the weekend that it was a mild, easily treatable form of cancer called a "basal cell carcinoma."

The disclosure ended several days of confusion about the nature of the growth, compounded by a White House news blackout on the issue Friday and conflicting or incomplete statements from the White House about whether a biopsy was performed to test for cancer cells.

While the health risk from this kind of skin cancer is minimal, the handling of information about the growth raised questions about the candor of presidential spokesmen concerning the president's health in the wake of his July surgery to remove a far more serious type of cancer found in his colon.

The skin cancer found on Reagan's nose is the most common cancer in the United States. Although precise numbers are unavailable, the American Cancer Society estimates more than 400,000 Americans each year are afflicted with skin cancer, most commonly of the highly curable type of basal or squamous cell cancers.

Basal and squamous refer to the type of skin cell affected. These cancers differ from a rare but deadly form of skin cancer known as malignant melanoma, which strikes about 22,000 people each year, spreads quickly and kills about 5,500 annually. In addition, there are about 1,900 deaths in this country from other types of skin cancer, but experts said that basal cell carcinoma is seldom the cause.

"The prognosis is excellent for basal cell carcinoma. It's rare it causes more than a cosmetic annoyance if it's taken care of when it's an early lesion," said Dr. Stephen Katz, chief of the dermatology branch of the National Cancer Institute.

Doctors said Reagan was at particular risk for getting skin cancer by virtue of his heritage and his life style. People with fair complexions, including those of Irish ancestry such as Reagan, compound their natural risk by extensive exposure to the sun.

Reagan, a southern Californian who has enjoyed the outdoors, said yesterday that the skin cancer discovery was a "a little heartbreaking for me to find out . . . because all my life I've lived with a coat of tan, dating back to my lifeguard days . . . . But now I'm told that I must not expose myself to the sun anymore." He said he didn't "mind telling you all this" if it would "convince people to stop broiling themselves n the sun." Reagan noted that his wife, Nancy, had a similar type of cancer removed from her upper lip in 1982.

Persons who have a basal cell carcinoma are at greater risk of getting another one elsewhere on the body, with the likelihood "anywhere from 25 to 50 percent within two years," said Katz. Again, the recurring cancers are easily removed and usually curative.

Experts emphasized that there was no connection between the development of cancer in Reagan's colon -- which his doctor said has a greater than 50 percent chance of being cured but poses a risk of recurrence -- and the development of the less harmful skin cancer. Reagan said yesterday that he had been bothered by the "pimple" before the July 13 colon cancer surgery and had picked at it; it was apparently irritated further by adhesive tape used to secure tubes during his recovery from surgery.

Extensive media coverage at the time of the colon cancer surgery may also have affected the White House's release of information last week when the skin growth was treated. Although the growth was removed last Tuesday at the White House, it was not until Thursday -- under questioning from reporters who noticed marks on the president's nose -- that White House spokesman Larry Speakes acknowledged that a small skin irritation on the right side of the president's nose had been removed.

Speakes initially told reporters that day that a biopsy to check for signs of cancer, would be "routinely" performed. But later Thursday his office issued a statement that said the tissue "was submitted for routine studies for infection and it was determined that no further treatment is necessary." There was no reference that time to a biopsy. Friday, Speakes declined to answer further questions about whether a biopsy was done, saying the statement late Thursday was "the final word." Also Friday, Jennefer Hirshberg, Nancy Reagan's press secretary, told United Press International the first lady had said no biopsy was done. It is unclear who knew that a biopsy was done. It was learned yesterday that some White House officials were aware last week that a biopsy was done. But Reagan said at his news conference yesterday that " . . . all the statements that have been made -- by Larry and by myself, by others -- have been the truth as we knew it. And I'm coming to a correction now, but we didn't know it at the time." He said he was told of the biopsy only when he got the results over the weekend at Camp David.

Hirshberg said yesterday that "Mrs. Reagan said neither one of them knew it was being biopsied. They learned of the biopsy this weekend."

Several experts, who emphasized that they were not familiar with details of Reagan's case, said it was standard procedure to do a biopsy when tissue is removed to make sure that cancer is not present.

"Obviously they must have done a biopsy to begin with," said Dr. Douglas Robins, a Washington dermatologist who was one of several doctors puzzled by the public comments last week. "It was very misleading," he said.

But Dr. Mervyn Elgart, chairman of the department of dermatology at the George Washington University School of Medicine, called questions about release of information on the president's care in regard to the skin growth a "tempest in a teapot. I think the president is entitled to his privacy except when it will affect the performance of his job . . . "