In addition to the trials and tribulations facing any dark-horse presidential hopeful, sometime before the Iowa caucuses next year, Marion G. (Pat) Robertson must face the perils of a legal trial challenging his honesty.

Robertson filed a libel suit last spring against former representative Paul N. (Pete) McCloskey (R-Calif.), with whom he served briefly when they were Marine Corps lieutenants during the Korean war.

McCloskey has asserted that Robertson, son of the late Sen. A. Willis Robertson (D-Va.), used his father's clout to have himself transferred from a troop ship carrying soldiers to the Korean fighting. Robertson says that is a lie.

U.S. District Court Judge Joyce Hens Green has ordered a jury trial. A date has not been set, but a likely time would be early January.

Thus, at a time when other presidential contenders are hobnobbing in Iowa, Robertson could find himself tied up for two weeks in a Washington courtroom, defending his integrity against several hostile witnesses.

Pretrial maneuvers in the case have brought out a great number of documents from Robertson's past, and facts that seem to help and hurt Robertson.

It has been established that Robertson's father wrote regularly on his Senate stationery to Marine officials about his son. The father also expressed concern that the young lieutenant had not been trained adequately for service in Korea.

It has been established that Robertson was pulled off the troop ship bound for Korea and assigned to duty in Japan for a while. He later went to Korea but did not see combat.

McCloskey has located several Marines who were on the troop ship and have said they felt or heard that Robertson had used parental clout to obtain the assignment in Japan. A former colonel recalls orders telling him to take care of a lieutenant whose father was a Virginia congressman.

But, so far, there is no direct evidence to prove McCloskey's charge that Robertson asked his father to get him out of combat.

Robertson has witnesses from the ship who are expected to testify that he was ready and willing to go to Korea. In depositions this spring, McCloskey backtracked somewhat from his original charge, saying that he could not clearly remember that Robertson claimed to have called his father to arrange a transfer.

Trial proceedings have prompted Robertson to modify his description of his Korean service. For years, he referred to himself as a "Marine combat officer." In depositions in the libel suit, he said he was in combat only in the technical sense of the term.

He said he served as an assistant adjutant, or administrative clerk, in a headquarters office and was never involved in fighting.