Lawrence M. Small, the embattled secretary of the Smithsonian Institution, has resigned, effective immediately, the Smithsonian announced today. Christian Samper, who directs the Smithsonian’s Museum of Natural History, will serve as acting secretary until a replacement for Mr. Small can be found.

Mr. Small had come under intense scrutiny in recent weeks for a lavish compensation package — more than $915,000 this year — and expenses that, according to news reports, topped $90,000 and included such items as chartered jets, catered meals, and a trip to Cambodia for his wife. A Smithsonian inspector general’s report concluded that although there was “no evidence of fraud or abuse,” some of Mr. Small’s expenses “might be considered lavish and extravagant.”

Since he took the job, in January 2000, Mr. Small has attracted controversy. Last year he signed a semi-exclusive deal with the Showtime cable channel, angering researchers who feared it would limit their use of Smithsonian collections. In 2004 he was sentenced to two years’ probation and 100 hours of community service after he purchased Amazonian tribal objects made with feathers from protected species for his personal collection. He drew criticism earlier for policies that cut back publishing at the Smithsonian Institution Press, that commercialized programming at the museums, and that sought to close a research center on museum conservation.

But under his leadership, the statement noted, the Smithsonian has raised more than $1-billion in private donations. In his letter of resignation, Mr. Small wrote that his tenure “has truly been a labor of love” and that he “spent countless days and evenings promoting the interests of the Institution.” —Jennifer Howard