Former sports car maker John Z. De Lorean boasted at a September meeting in Washington that he had "an intimate relationship with the Irish Republican Army" and that the terrorist group was helping finance his cocaine-trafficking scheme, according to documents filed here today in federal court.

The declaration by Assistant U.S. Attorney James P. Walsh Jr. was filed to support his refusal to identify, until the trial, a government informer crucial to the federal case against De Lorean, 57, who has been charged with nine counts in an alleged drug-trafficking scheme.

"Based upon De Lorean's admitted close relationship with the IRA and the well-known propensity of narcotics violators to commit violence against government witnesses, particularly informants, the government declines to furnish the identity of any informant in this case at this time," the declaration said.

It was the first time that the terrorist group has been mentioned in connection with the case. The De Lorean Motor Co. was based in a militant Irish nationalist neighborhood of Belfast until it was closed by the British government last fall for lack of funds. The building was firebombed in 1981.

Neither De Lorean nor his attorneys could be reached for comment.

Walsh said he had seen a videotape of a Sept. 4 meeting at the L'Enfant Plaza Hotel in Washington in which De Lorean and the informer, identified by sources as aircraft salesman James T. Hoffman, discussed " . . . Options for allowing De Lorean to realize a large amount of money by means of several narcotics deals involving both cocaine and Asian heroin."

"During the course of that meeting, John De Lorean boasted of an intimate relationship with the Irish Republican Army. De Lorean claimed that the IRA was a partial sponsor of 'our projects' and that the IRA were 'our protectors.' De Lorean further stated that the only reason that he was able to survive in 'the most difficult terrorist area in all of Northern Ireland' was because of a 'very tight relationship with the IRA.' He also stated that he was getting the money to finance the narcotics deal from the IRA."

Walsh said De Lorean spoke "in the context of a threat, that his interests would be protected by the terrorist strength of the IRA."

Walsh said that in another taped conversation De Lorean said "his contact man in the IRA had come into the United States to check on arrangements for the financing of the load of narcotics."

In other papers filed today, prosecutors said they had given attorneys for De Lorean and his major co-defendant, aircraft company owner and alleged cocaine transporter William Morgan Hetrick, more than 100 audio and video tape recordings of meetings in the scheme, which also involved undercover agents for the Drug Enforcement Administration and the FBI.