About 2,000 shipments a year are refused entry to the United States, based on these inspections or other issues; the highest share of those blocked come from China, India, South Korea, Canada and France, the letter said. Imports from China were particularly problematic — as has historically been the case with other products, including children’s toys. Cosmetics imports from China have jumped 79 percent over the last five years, the letter says.

For example, samples examined by the F.D.A. of a Chinese-made product called Kleancolor Frameous Lash & Brow, which sells for just $1, contained hazardous levels of mold, given that its intended area of use was the eye. The F.D.A. also found dangerous levels of mercury — it can cause kidney and nervous system damage — in a product made in Mexico called “Crema Piel De Seda,” or “Silky Skin Cream.” It was marketed to whiten skin, treat acne and remove various skin blemishes.

, The real problem was that the agency has no way of knowing how widespread the problem is with imported cosmetics, given that it is doing so few inspections, said Deborah Kotz, an F.D.A. spokeswoman. But she said that the agency inspects only imported cosmetics it has a reason to suspect might have problems, which inflates the rate of adverse findings. The 20 percent adverse-findings figure does not mean that the problem is that widespread in imported cosmetics over all.

“The F.D.A. believes that the vast majority of cosmetic products on the market are safe, but our information on the universe of cosmetics is limited,” said Linda Katz, director of the office of cosmetics and colors, in a written statement.

Mr. Pallone, in an interview, said that the data the F.D.A. provided could help convince Congress to take up legislation to strengthen regulation of imported cosmetics. The idea has been embraced by some congressional Republicans as well as many major companies in the industry, who could benefit if cheap imports (including sometime counterfeits of their brand-name products) are subject to more scrutiny.

“The time is ripe to deal with the cosmetic issues, given the problems with imports,” Mr. Pallone said. He intends to reintroduce his proposal to expand the regulation of cosmetics, including imports, as part of a larger bill that would fund greater oversight of over-the-counter drugs.