During the moratorium, some of its equipment deteriorated, nuclear experts believe. Iran has yet to complete the crucial piping system needed to move uranium gas from one centrifuge to the next. Until the latter step is complete and the system is sealed, enrichment cannot begin. Experts disagreed over how long those next steps could take. ‘‘This is the next rung on the technical ladder,’’ said David Albright, a former weapons inspector who is now president of the Institute for Science and International Security in Washington.

Iranian leaders insist that they are trying to gain the knowledge necessary to make enriched uranium for civilian uses. While it is technically possible to manufacture enough highly enriched uranium for a bomb using a 164-centrifuge cascade, the process would take 10 years. Weapons experts do not think that is Iran’s plan. Instead, the experts say their concern is that running a small cascade would give Iran the technical knowledge to build and operate a far larger one. — Alissa J. Rubin