TECHNICALLY, the dismissal of Oliver North's Iran-contra convictions and the opening of CIA-director-designate Robert Gates's confirmation hearings - in which the Iran-contra scandal figures prominently - have nothing to do with each other.Colonel North's convictions were thrown out Sept. 16 because special prosecutor Lawrence Walsh could not prove that the convictions were not influenced by the 1987 testimony North gave to Congress while under immunity from prosecution. In contrast, Mr. Gates's Iran-contra ordeal is far from over. As the focus of Walsh's investigation has moved to the upper levels of CIA management, where Gates served as deputy director of Central Intelligence when the affair unfolded, Gates's pleas of noninvolvement are receiving increasing skepticism. The dismissal of North's convictions does not directly affect Gates's case before the Senate Select Committee on Intelligence. Gates, as before, remains a "subject" though not a "target" of Walsh's continuing investigation. But in a broader sense, the news about North - who, after all, masterminded the arms-for-hostages deal with Iran and diverted the profits to the Nicaraguan contras - can't help but alter the political air in which the Gates hearings take place. North's fortune furthers the notion that Iran-contra is history rather than a current event. Indeed, the opening day of hearings showed a majority of intelligence committee senators inclined for now to give Gates the benefit of the doubt. And barring any revelations between now and a full Senate vote on his candidacy, Gates seems to have a greater than 50-50 chance of being confirmed, Capitol Hill analysts say. The intelligence committee's lack of access to information being collected by a grand jury investigating the scandal makes it all the harder for committee members to get to the bottom of the matter at Gates's hearings. Walsh's investigation could last as long as five more years, and the committee leadership decided it could not delay any further the installation of the United States' new intelligence chief, especially at a time of historic transition in the post-cold-war order. Time seems to have served Gates well. Four years ago, when he withdrew his nomination for the same position amid questions about his role in Iran-contra, Gates's brilliant rise up the CIA ranks appeared over. Two months ago, when a Gates subordinate at the CIA suddenly pleaded guilty to lying to Congress about Iran-contra, the Gates hearings were postponed - and the betting on Capitol Hill was that Gates's name would be withdrawn again. But with the changes in the Soviet Union and discussion of a radical restructuring of the nation's intelligence services now all the more current, the strong suit in Gates's nomination - his intimate knowledge of both the intelligence community and the White House - gives him particular appeal among many senators. But in his first day of questioning, Gates did not get off easy with every senator. Sen. Howard Metzenbaum (D) of Ohio voiced incredulity that Gates could have been as ignorant as he claims of the Iran-contra scheming going on around him. "You were absolutely surrounded by the truth; how could you possibly not know?" Senator Metzenbaum said. "As No. 2 man at the agency, such willful ignorance is inexcusable." Sen. Bill Bradley (D) of New Jersey charged Gates with "persistently" overstating Soviet intentions and with giving unauthorized support to secret Israeli shipments of arms to Iraq without disclosing them to Congress for a full year.