The Obama administration on Monday defended its decision to negotiate with North Korea as the reclusive regime prepared for a long-range rocket launch and a possible nuclear bomb test — two actions that fly in the face of the deal the United States struck recently with leaders there.

With fresh evidence released by South Korean intelligence on Sunday suggesting that the North plans an underground nuclear test, U.S. officials who began the year with tentative optimism about their engagement with Pyongyang are instead scrambling to find ways to express their disapproval of an already heavily sanctioned government.

“There’s a lot of ‘shoulda, ­coulda, woulda’ now from outsiders,” said a senior administration official who was not authorized to speak for attribution. “But the fact is that we went into this carefully with a specific purpose in mind.”

Critics say that by striking a deal in February to provide food aid in return for a ban on missile and nuclear tests, President Obama did more harm than good. Once the rocket is launched, North Koreans could use the ensuing condemnation from the United States and other countries to justify an action such as a nuclear test as retaliation, as they have in similar situations in the past.

“Any administration could have had trouble with this, but I think there’s legitimate worry that this is now all going to literally blow up in their faces,” said Victor Cha, who served as director for Asian affairs on the National Security Council under President George W. Bush. “Obama could be seen as the guy who tried engagement and ended up getting more missile tests and nuke tests under his watch than Bush.”

“We seem to have jumped in with eyes wide shut,” said Michael Auslin, an Asia expert at the American Enterprise Institute, a conservative think tank. “Now you not only have a crisis with the rocket launch, but a diplomatic failure that sets the tone for the next decade with this new young leader in North Korea, who on his very first attempt to tweak the lion’s tail may only see that he can get away with it.”

Obama administration officials, however, argued that their deal with North Korea was a necessary, deliberate test to probe how serious North Korea’s new leader, Kim Jong Eun, is about reaching a detente with Washington and resuming talks on denuclearization.

For two years, the Obama administration held firm to its position of refusing to talk to North Korea until it demonstrated its seriousness by adhering to previous commitments. The United States resumed engagement in recent months because the North indicated it might be willing to agree to a moratorium on nuclear and missile tests.

Much of the criticism from analysts, including past negotiators and former Republican White House officials, has centered on whether the United States spelled out in clear enough terms that a satellite launch, such as the one North Korea plans to conduct between April 12 and April 16, would violate their deal.

In interviews on Monday, senior administration officials could not say definitively whether they raised the issue of satellites, but they said they had warned North Korea explicitly and in detail about space launches.

The agreement resulted in official statements from both sides but no signed deal. No food was transferred before the agreement unraveled.

“We made a specific point of laying out [that] any sort of space launch would be a deal-breaker,” said one senior administration official. “We know they heard it too because they repeated it back to us.” While some news reports have suggested that the North Koreans told U.S. negotiators ahead of the Feb. 29 agreement about their plans to launch a satellite, U.S. officials said Monday that this issue was never disclosed or discussed.

The North is arguing that the three-stage rocket launch is a peaceful civilian project to put a satellite into orbit and that it has the right, under an international space treaty, to conduct such a launch for peaceful purposes. Officials in Washington, Seoul and Tokyo say the launch is a thinly veiled cover for Pyongyang to test its ballistic missile technology.

On Tuesday, North Korean space officials rejected such claims as “nonsense” after showing a team of foreign journalists the three stages of the rocket in position at a launch site.

South Korea’s Ministry of Unification, which is in charge of policy toward Pyongyang, on Sunday sent a report to journalists detailing activity at a test site in North Korea’s northeast, the location for nuclear tests in 2006 and 2009. The report, citing recent commercial satellite images, said that the North is “on its way to another grave provocation” by gathering dirt at the entrance to a tunnel.

According to the analysis, that dirt would be used to plug the tunnel before conducting an underground test, which would be the North’s third.

“The effort is believed to be in its final stages,” said the report, which was drafted by Seoul’s intelligence agency. “The soil around the tunnel’s entrance appeared to have been brought in from another region and has been growing in amount since March.”

If North Korea conducts a nuclear test soon after launching its rocket, it would match the pattern set in 2006 and 2009, when similar launches brought international condemnation. In both cases, Pyongyang, expressing outrage at the response, tested nuclear devices soon after.