Even before the Justice Department received a copy, Bantam Books had it all set in type.

The merchandising of the final report of the House Assassinations Committee began in a rush last Friday, while the rest of the world was still awaiting formal release of the panel's findings in the murders of President Kennedy and the Rev. Martin Luther King Jr.

After negotiations with chief committee counsel G. Robert Blakey, a representative of the book publishing company was provided with an exclusive advance copy that day, to pave the way for another instant book.

It will feature, among other things, "an exclusive introduction" by Blakey for a fee said to be somewhat less than $3,000. A Bantam publicist proudly displayed a copy of the forthcoming paperback's cover to reporters yesterday at a news conference shceduled by House committee members to make public the government-printed version of the findings. After a few moments, Blakey frowned and sent word for the man from Bantam to stop.

One of the central recommendations of the House committee, which wound up its $5.4 million inquiry with a series of iffy findings about a gangland plot to kill Kennedy and a racist bounty to kill King, was that the Justice Department review its work and continue the investigation.

As Blakey, who so far has insisted on not being quoted by reporters about the report, puts it in his work for Bantam:

"It is up to the government - the $&(WORD ILLEGIBLE executive branch, specifically that department called "Justice." The committee has provided a road map that indicates the points of departure for subsequent investigation that need not be limited to congressional investigations are - New Orleans, in the case of the Kennedy assassination; St. Louis, in the case of the King assassination. The government, to live up to the meaning of "Justice," can do no less than to pursue the course the committee has charted."

The Justice Department remains noncommittal, at least partly because it has yet to receive a copy of the report. Department spokesman Robert Havel said a check yesterday afternoon showed it had yet to arrive.

Bantam's 736-page edition, meanwhile, had been set in type in Nashville and was, at that moment, on the way to printers in Chicago, according to associate publicity manager Terry Bromberg. Price at $3.95 - in contrast to the Government Printing Office price of $6.50 - it should be on newsstands in selected cities such as Washington by Monday, if not sooner, he said.

Besides the special introduction by Blakey, it will feature a 2,500-word foreword by Tom Wicker, associate editor of the New York Times. Wicker did not cover the Assassinations Committee's hearings nor did he get a copy of the final report until Tuesday afternoon, with the rest of the press. Bantam's early copy went straight to Nashville over the weekend, with no time to make a copy of it for Wicker.

Even so, Bromberg reported, Wicker, who was present at the JFK assassination, spent the weekend fruitfully, "starting with a personalized account from Nov. 22, 1963, forward" and finishing Tuesday night with a hurried reading of the House committee's report. It was made public Tuesday - instead of yesterday as originally scheduled - because The Times published a preliminary account of the committee's work Tuesday morning.

At yesterday's news conference for the now defunct House committee, Chairman Louis Stockes (D-Ohio) confirmed that he had authorized early release of a copy for commercial printing, but skirted a question about the propriety of that action.

Blakely refused to comment when asked if he had been paid for writing the introduction.

Bantam spokesmen later said he had been given "an honorarium of under $3,000." Conclukded Bromberg: "So he's not making off like a bandit by any means."

At another point in the news conference, Blakely was asked whether he thought organized crime was responsible for John Kennedy's death.

"I have no public views to state," Blakely replied. CAPTION: Picture, Joseph J. Kelly, an engineer for Babcock & Wilcox, testifying yesterday. AP