VIENNA, Austria – The chief U.N. atomic watchdog chided Iran yesterday for delays in divulging key information about its nuclear program, saying the onus is on Tehran to overcome a “confidence deficit” caused by past cover-ups.

As Mohammed ElBaradei criticized Iran at a meeting of the International Atomic Energy Agency, the Bush administration suggested it was considering a major strategy shift – joining Europe in offering Tehran economic incentives to abandon its uranium enrichment program.

Russia, meanwhile, sought to dismiss concerns that an Iranian nuclear reactor it built and will supply with fuel could be used to develop weapons. An accord signed Sunday is key to bringing Tehran’s first reactor on line.

The deal was struck despite American objections, although American officials said they could live with the pact because it was designed to eliminate the possibility of the Iranians misusing the fuel for weapons.

More worrisome for American and European nations are Iran’s plans to enrich its own uranium.

While Iran says it wants the technology only to generate electricity, the process can also produce weapons grade material for warheads, and Washington contends that is the main reason Tehran is interested in enrichment.

Iran has suspended work on enrichment pending negotiations with France, Germany, and Britain but has repeatedly said the freeze is of short duration, despite European hopes that Tehran will commit to fully scrapping its program.

A two-year investigation by the U.N. nuclear agency established that Iran ran a clandestine nuclear program, including uranium enrichment, for nearly two decades.

In a new revelation of Iran’s past covert activities, diplomats said over the weekend that as early as 1987 Iran had received a written offer from a nuclear black market network to set up the basics of an enrichment program. They said the Iranians turned over the list to the agency only recently.

Alluding to such delays in revealing illicit activities, Mr. ElBaradei spoke of Tehran’s “confidence deficit” and said only better cooperation from the Iranians would “build the necessary confidence” to dispel concerns about their nuclear aspirations.

Iran and North Korea are considered the greatest nuclear threats and the board’s meeting this week will focus on them. The agency has little leverage with North Korea, which quit the agency two years ago and claims to have atomic weapons, but diplomats said the board likely would urge the communist state to return to six-nation talks meant to defuse the threat.

The question of how to deal with Iran’s nuclear program has brought two years of stormy sessions for the Vienna based agency’s board, but that tension was absent yesterday.

During President Bush’s trip to Europe last week, leaders there urged him to join them in offering economic incentives such as eventual membership for Iran in the World Trade Organization. They argued a united front would be more effective than a continuing American-European split over how to deal with Iran.

Signaling a possible American shift, White House spokesman Scott McClellan said yesterday that Mr. Bush “is thinking through some of the ideas that were discussed.”

The European approach – offering a carrot to Tehran now along with the stick of harsher actions if necessary – had been flatly rejected by the administration ahead of the European trip.