(Rewrites with Justice Department timeline)

NEW YORK/WASHINGTON April 24 (Reuters) -

U.S. Department of Justice officials are planning to decide as soon as late May whether Boeing violated an agreement that shielded the planemaker from criminal prosecution over fatal crashes in 2018 and 2019, people familiar with the matter said.

Justice Department officials revealed the timeline in a closed-door meeting on Wednesday where families of the victims of the two Boeing 737 MAX crashes pressed U.S. officials to criminally prosecute the planemaker.

The families have argued that Boeing violated a 2021 deal with prosecutors to overhaul its compliance program following the crashes, which killed 346 people.

Federal prosecutors had agreed to ask a judge to dismiss a criminal charge against Boeing so long as it complied with the deal's terms over a three-year period.

A panel, however, blew off a new Boeing 737 MAX 9 jet during a Jan. 5 Alaska Airlines flight, just two days before the 2021 agreement expired.

Justice Department officials are now weighing that incident as part of a broader probe into whether Boeing violated the deal, known as a deferred prosecution agreement, or DPA, two people familiar with the matter told Reuters.

A government official at the Wednesday meeting said the Justice Department will likely decide by the end of May if they believe there was a breach or not, two sources told Reuters.

If the DOJ decides there was a breach, they would have another meeting about the next steps, such as extending the DPA, negotiating a guilty plea or taking the case to trial, the sources said.

Family members argue an independent monitor is needed to ensure Boeing's compliance with the agreement. Boeing's deal had no such requirement, unlike some past agreements with other companies.

Boeing was not immediately reachable for comment, while the Justice Department declined comment.

In January 2021, Boeing agreed to pay $2.5 billion to resolve a criminal investigation into the company's conduct surrounding the crashes. The U.S. planemaker agreed to compensate victims' relatives and overhaul its compliance practices as part of the deal with prosecutors.

In an earlier April meeting with family members' lawyers, Justice Department officials said they were looking at circumstances outlined in the 2021 deal that could put Boeing in breach of the agreement, such as the company committing a felony or misleading U.S. officials, one of the people familiar with the matter said.

The agreement gives U.S. officials six months from the deal's Jan. 7 expiration to decide whether to prosecute Boeing on a charge that the company conspired to defraud the Federal Aviation Administration or pursue other alternatives to dismissing the case.

Officials plan to do so within that time frame while investigations into the Jan. 5 in-flight blowout continue, which could inform their decision, one of the people said. The people spoke on condition of anonymity.

Prosecutors are expected to lean heavily on findings from the FAA's investigations, one of the people previously told Reuters.

The FAA, for instance, is investigating a Boeing engineer's claims that the company dismissed safety and quality concerns in the production of the planemaker's 787 and 777 jets.

In a congressional hearing last week, the engineer testified that Boeing sidelined him when he raised concerns. Reuters has not independently verified his claims, which Boeing has disputed.

(Reporting by Mike Spector in New York and David Shepardson in Washington; Additional reporting by Allison Lampert in Montreal and Chris Prentice in New York; Editing by Jonathan Oatis and Marguerita Choy)