Former White House aide Lyn Nofziger was described yesterday by independent counsel James C. McKay as guilty -- "not just beyond a reasonable doubt, but beyond a shadow of a doubt" -- of cashing in on his influence in violation of federal conflict-of-interest law.

Nofziger's lawyers, in turn, accused the prosecution of unfairly singling him out for a few inconsequential lobbying contacts and creating a world "where a single memo gets blown out of proportion."

The sharply conflicting assessments came in closing arguments at the trial of Nofziger and codefendant Mark Bragg, his partner in a Washington consulting firm. The jury is scheduled to begin deliberations today.

Nofziger and his lawyers might try to dismiss the charges as insignificant contacts, McKay told jurors at the windup of the 16-day trial in U.S. District Court, but he urged them to remember the attention and access that Nofziger commanded as a longtime confidant of President Reagan.

"This is not a nobody," McKay declared. "It's Mr. Lyn Nofziger who indisputably is a close friend of the most powerful people in the administration, including the president of the United States. Lyn Nofziger -- a man to be reckoned with!"

Nofziger was charged with felony counts of illegal lobbying at the White House in 1982, twice for the now-bankrupt Wedtech Corp. and twice for other clients, the Marine Engineers Beneficial Association (AFL-CIO) and Fairchild Industries. Bragg has been standing trial with him on one count of aiding and abetting.

The case is the first major test of the 1978 law prohibiting former high-ranking officials from lobbying their old agencies for a year after leaving on any "particular matter" that is of "direct and substantial interest" to the agency.

Nofziger lawyer E. Lawrence Barcella maintained that McKay and his prosecutors had, in effect, set up a telescope on the White House lawn for the year 1982 and focused "on a minuscule part, in most cases, of what was going on" there, seizing on a few scattered Reagan campaign promises and directives as though they were "gospel."

"Just because something may float through the White House for a brief period of time doesn't make it important, doesn't make it of 'substantial and direct interest,' " Barcella said.

McKay, however, argued that the case was really a rather straightforward one, with Nofziger improperly barreling in on issues that Reagan, by his own pronouncements, and some of his top aides, by their actions, had clearly brought within the purview of the conflict-of-interest rule.

The law, McKay added, does not require that such lobbying actually be successful. The law is broken, he said, when the attempt to influence occurs.

"Like it or not, that's the law," McKay told the jury. "That's prohibited. It's not up to us to say if it's a bad law."

The first count, against Nofziger alone, involves an April 8, 1982, memo he sent to then-presidential counselor Edwin Meese III, warning Meese that "it would be a blunder" not to give Wedtech an Army engine contract it was seeking despite Army complaints about Wedtech's prices.

The reason for that warning, McKay pointed out, was that Reagan had stood on a South Bronx street corner during the 1980 campaign, not far from the Wedtech plant, and, with Nofziger present, made a promise to revitalize the area, a promise that Reagan noted President Jimmy Carter had also made but failed to keep.

In his memo to Meese, Nofziger had said " . . . Awarding the contract to Welbilt {Wedtech's old name} would be a major first step in the president's commitment to revitalize the South Bronx."

"Here's the attempt to influence," said McKay of Nofziger who had been hired by Wedtech a month or two earlier. "It's an obvious effort to take advantage of his influence with Ed Meese."

Barcella likened the approach to that of "a traveling salesman coming by your door to see if you want to buy encyclopedias and maybe getting a polite reply, maybe getting a smile." If the White House had had "a direct and substantial interest" in a contract for Wedtech on April 8, 1982, he argued, "the memo wouldn't have been necessary."

Barcella also took exception to the charge that Nofziger had been "cashing in" and asserted that Nofziger's only reward for leaving the White House to make a better salary was "the felony counts in this indictment."

The disputes over the other charges boil down to similar questions of whether the causes Nofziger was promoting were of "direct and substantial interest" at the White House. But the second Wedtech count also involves sharp disagreement over whether Nofziger, then recuperating from a mild stroke, actually signed a May 28, 1982, letter as alleged and whether it was sent to the White House by mistake or by design.

"The prosecution hasn't proved any of its charges, not one of them," Barcella maintained. "It's time for this yearlong nightmare of Lyn Nofziger's to come to an end -- so that he and his wife can go home and put their lives back together."