Baghdad, Iraq ? A strengthened corps of U.N. inspectors broadened its scrutiny of Iraq’s military-industrial complex on Wednesday, probing deeper into a nuclear research center and a desert uranium mine, and making a spot inspection of a new missile factory.

At one site where Iraq once sought to enrich uranium to nuclear-bomb quality, inspectors verified Wednesday that nuclear activities have not been revived, the U.N. inspection agency reported.

As the field teams began their third week of operation in Iraq, their analytical support staffs in New York and Vienna were studying Iraq’s huge new arms declaration in search of still more sites to visit and questions to answer.

In the coming months, U.N. officials hope to inspect hundreds of Iraqi industrial and research installations, many of them “dual-use” sites whose products or equipment could be devoted to either civilian or military use.

To help accomplish that, 28 new inspectors flew Tuesday to Baghdad, bolstering the U.N. operation to 70 inspectors, and U.N. technicians readied the first of eight helicopters expected to join the monitoring effort. The helicopters will not only provide transportation; at times they may take air samples or sweep areas with radioactivity sensors.

The United Nations hopes to have up to 100 inspectors at work in the field each day by late December. They come from both the Vienna-based International Atomic Energy Agency (IAEA) and the U.N. Monitoring, Verification and Inspection Commission, UNMOVIC, whose inspectors specialize in chemical and biological weapons and missiles.

The inspections resumed Nov. 27, after a four-year gap, under a new U.N. Security Council resolution mandating that Iraq surrender any weapons of mass destruction — which it denies it has — and report on nuclear, biological and chemical research and production. That declaration, totaling 12,000 pages, was filed over the weekend.

One of at least eight sites checked Wednesday was al-Tuwaitha, Iraq’s major nuclear research center, where U.N. experts continued thorough inspections begun earlier in the week.

In the 1980s, scientists at al-Tuwaitha, 15 miles southeast of Baghdad, were key to Iraq’s efforts to build nuclear weapons. Many of the complex’s more than 100 buildings were destroyed in U.S. bombing during the 1991 Gulf War. The IAEA inspectors were checking for any signs of revived Iraqi interest in nuclear weaponry.

Inspectors were able on Wednesday to verify there is no such revived interest at another site, the Ibn Sina Company at Tarmiya, 25 miles north of Baghdad, the inspectors’ Baghdad office reported. In the 1980s, Iraqi scientists and engineers at Tarmiya had sought unsuccessfully to master a technology — called electronic magnetic isotope separation — to enrich uranium to fissionable levels usable in atomic bombs.

Another team Wednesday drove to an industrial zone north of Baghdad to inspect a factory belonging to al-Karama, a company long involved in missile production. Under U.N. resolutions adopted after Iraq’s defeat in the Gulf War, Iraq may not possess missiles with a range greater than 90 miles.