Lyn Nofziger, a long-distance loyalist who waited 14 years for his man to become president, goes on trial in U.S. District Court this week on charges of illegal lobbying. Jury selection is scheduled to start today before U.S. District Court Judge Thomas A. Flannery.

The trial of the former top aide to President Reagan promises to be hard-fought. It will be the first major test of the Ethics in Government Act's "one-year rule" banning former high-ranking government officials from lobbying at their old agencies on certain matters within a year after leaving.

According to informed sources, prosecutors for independent counsel James C. McKay proposed that Nofziger plead guilty to a single count in return for dismissal of all other charges against him and against his partner, Mark Bragg, who was indicted for aiding and abetting. Nofziger, the sources said, refused, not once, but twice.

"If they want to make me a felon, they're going to have to prove it," one acquaintance of Nofziger quotes him as saying.

The prosecution contends it has a solid case. And in pretrial hearings stretching back to last summer, it has prevailed on almost every contested issue.

Nofziger contended that the one-year rule was an unconstitutional restriction of his right to free speech. Flannery rejected the complaint.

Nofziger claimed he had no criminal intent. Flannery held that the law is a "public welfare" statute. It was Nofziger's duty, the judge said, to find out what his obligations were.

Nofziger said he sought the advice of counsel. The judge ruled that what lawyers might have told him was no excuse.

Even simple facts are in dispute. Nofziger, who left the White House in January 1982 to go into the consulting business, faces trial on four felony counts of illicit lobbying, twice on behalf of the Wedtech Corp., twice more on behalf of other clients, Fairchild Industries and the Marine Engineers Beneficial Association (MEBA), a labor union.

The most publicized charge concerns Wedtech and its efforts in 1982 to win a no-bid $32 million Army engine contract. The company nailed down the award following a May 1982 White House meeting arranged by James Jenkins, top deputy to Edwin Meese III, who was the president's counselor. Bragg attended the session. A few days later, Jenkins received a follow-up letter signed by "Lyn," asking for Jenkins' help in securing a letter of intent from the Army.

Nofziger has said he cannot remember signing the letter. His lawyers have said the government will have to prove that he did. An FBI handwriting analysis conducted last July was inconclusive.

Bragg was indicted on a single count because of his alleged role as a middleman in this incident. His lawyers say it was Jenkins who suggested, in a telephone call to Bragg, that Wedtech obtain such a letter from the Army so that the company could use it to get additional funding from another agency.

Another charge against Nofziger involves a letter Nofziger sent to Meese on April 8, 1982, about the contract Wedtech was seeking. Meese has said that it was he who ordered the 1982 White House review of Wedtech problems to make sure, he said, that the company received "a fair hearing."

According to the prosecution, Bragg did the day-to-day lobbying for Wedtech, invoking Nofziger's "name and influence" in the process. "When he thought it was critical to the engine contract," the grand jury charged, Bragg persuaded Nofziger to weigh in "personally and directly."

The two final counts in the indictment revolve around an Aug. 20, 1982, letter Nofziger is accused of sending to Jenkins as a MEBA lobbyist about expanding the use of civilians aboard U.S. government ships, "an initiative that was promoted by the president," and a Sept. 24, 1982, meeting as a Fairchild lobbyist with the National Security Council staff about continued production of the imperiled A10 antitank aircraft.

Two other charges were brought against Nofziger last July, accusing him of violating a lifetime lobbying ban by promoting Wedtech's interests with the Army and the Small Business Administration after Nofziger had allegedly worked on Wedtech matters at the White House. But McKay dropped those charges last month. Prosecutors said they dismissed the two counts to make the case "simpler," but Nofziger's lawyers contend the step was taken because there was no proof he had done anything for Wedtech until leaving the government.