He replaces Bill Bavasi for the short, and possibly, long term.
When he announced the dismissal of Bavasi, Mariners CEO Howard Lincoln said the search for a permanent GM would begin immediately, and Pelekoudas is a candidate for the position.
"Chuck and I have confidence in Lee Pelekoudas, who has been with the Mariners for many years, and who is a respected baseball executive," Lincoln said. "As interim general manager, Lee will be responsible for all aspects of our baseball operations department."
Armstrong said his search could be impeded a little because of the timing.
"We are basically in the middle of the season and perhaps some of the best candidates are already involved with their clubs in the middle of a pennant race," he said. "We can't disrupt other clubs as this time, and so, as far as the timeline, I would think that this may well go into the offseason before we make our final decision."
Pelekoudas was a candidate the last time there was a GM vacancy. That was almost five years ago, when Bavasi was selected, and the outgoing front-office executive said during his farewell to the media session at Safeco Field Monday that his right-hand man definitely is ready to take the baton.
"Lee is as ready for this now as he was when I got this job," Bavasi said. "Lee can handle it. He has been in the game as long, or longer, than I have and I think he is well-suited for this situation. He can focus on the Major League club."
Bavasi leaves behind a solid front-office team, which includes player personnel director Benny Looper; international operations director Bob Engle; scouting director Bob Fontaine; special assistants to the GM John Bowles, Ken Madeja, Duane Shaffer and Dave Wallace; and director of player development Greg Hunter.
Most of them were hired by Bavasi during his four-plus seasons with the Mariners.
"I hope the people here stay here," Pelekoudas said on Monday afternoon. "Bill brought them in for a reason and they are all good people. As the interim GM, I don't foresee making any changes there at all. I value their judgments and they are valuable people to have."
Armstrong will be in charge of finding Bavasi's permanent replacement, a task the club president could take until the end of October to complete.
Armstrong said he would consult with numerous contacts he has developed during his 23 years in baseball, including Commissioner Bud Selig, when putting together a list of candidates.
"We will leave no stone unturned," he said. "I think it's good to get outside, objective, third-party opinions on what other knowledgeable people in baseball perceive what the Mariners are doing right, what they're doing wrong. There are a lot of smart people out there and I look forward to talking with them.
"I certainly don't have all the answers right now. I'm trying to formulate what the correct questions are."
Armstrong's list could include former MLB general managers Dan O'Brien and Wayne Krivsky and David Forst, the Athletics' assistant GM.
The son of a former National League umpire and father of two sons, Chris and Bryan, who currently work for MLB organizations, Pelekoudas has strong baseball roots. He was drafted by the Expos in the 23rd round of the 1969 First-Year Player Draft out of Homestead (Calif.) High School, but elected to attend college at Arizona State and earned a degree in journalism in 1973.
His late father, Chris, was an NL umpire for 16 years.
Pelekoudas said he was "surprised" that the general manager change was made and his first reaction had nothing to do with his own status but that of his boss and friend.
"Bill is a good man," he said. "In my estimation, and a lot of people's estimation, he did a good job. I felt bad for Bill. That was my first emotion."
Going forward, Pelekoudas will now shift into a high-speed gear and get to work on fixing a team that rests at the bottom of the American League West with the worst record in the Major Leagues.
"We have to figure out what's wrong and go forward," he said. "This team is flat-out underperforming. The talent is much better than what has been shown on the field. Is it bad luck? I'm not going to say, but there must be something causing this."
He left little doubt that he would like the "interim" to be dropped from his new title.
"I think any time you get a chance to run a club, it's an opportunity you go for," he said. "Obviously, this is not the circumstances you want to get a job under. These are trying circumstances, not only because the ballclub is struggling right now, but to take the place of a good friend who has treated you well is an awkward situation.
"If you're serious about this game, you know what you have ahead of you. It's a tough job, and you either do the job or you don't. All you can do is the best job you can and have confidence in what you are doing."