WASHINGTON — Representative Trey Radel, Republican of Florida, announced late Wednesday that he would take a leave of absence from office after pleading guilty earlier in the day to a misdemeanor charge stemming from his purchase of cocaine here last month. He was sentenced to one year of probation.

Mr. Radel said his “team” in Washington and in his southwest Florida district would take of his congressional business while he received what he called “intensive in-patient treatment.”

“I want to be a better man for southwest Florida,” Mr. Radel said in a 10:30 p.m. news conference in Florida. He added that he would donate his salary to charity while he was away.

According to documents released by prosecutors, the federal authorities learned this fall that Mr. Radel, a freshman legislator, had bought cocaine on several occasions for his own use in Washington and had sometimes shared it with others.