In what would be a significant concession, Obama administration officials say they could support allowing Iran to maintain a crucial element of its disputed nuclear program if Tehran took other major steps to curb its ability to develop a nuclear bomb.

U.S. officials said they might agree to let Iran continue enriching uranium up to 5% purity, which is the upper end of the range for most civilian uses, if its government agrees to the unrestricted inspections, strict oversight and numerous safeguards that the United Nations has long demanded.

Such a deal would face formidable obstacles. Iran has shown little willingness to meet international demands. And a shift in the U.S. position that Iran must halt all enrichment activities is likely to prompt strong objections from Israeli leaders; the probable Republican presidential nominee, Mitt Romney; and many members of Congress.