Forwards Malkin and Rust, and defenseman Letang can each become an unrestricted free agent after the season. Hextall said keeping them would depend on if their contracts could fit under the NHL salary cap.
"We've had discussions, but I don't negotiate publicly," Hextall said. "We've had discussions with those guys, and certainly they're a top priority for us. We have a limited amount of cap space, so to squeeze everybody in is certainly our goal. Whether it's possible or not, I don't know.
"With every player, there's a certain number you feel like you can go to and that's where you draw the line. But negotiations have been fine. We'll continue on."
Malkin and Letang, each in his 16th season with the Penguins, won the Stanley Cup three times (2009, 2016, 2017). Rust, who is in his eighth season with Pittsburgh, was part of the 2016 and 2017 championships.
Malkin, 35, is second in Penguins history in games played (949) behind Sidney Crosby (1,070). He is third in points (1,114) and assists (686), and fourth in goals (428).
Letang, 34, is first among Pittsburgh defensemen in goals (139), assists (481), points (620) and games played (902).
"I think 'Geno' and [Letang], they've been here for, I think, 16 years," Hextall said. "I know they've done a lot for the city. The city's been good to them. So it's certainly a match that we'd like to continue on with, but obviously the players have choices too. We'll see where they are."
Malkin missed the first 34 games this season after having knee surgery June 4. He has scored 10 points (four goals, six assists) in nine games.
Malkin recently said he would like to play another three or four seasons. The second-line center also said he wasn't concerned with being in the final season of an eight-year, $76 million contract ($9.5 million average annual value) he signed June 13, 2013.
"I'm not thinking about my contract right now," Malkin said Dec. 29. "I'm not thinking about money. I'm a pretty rich guy. ... This is my point, I have had a tough half of the year. I want to be back at my level of my game."
The Penguins (27-10-6) have won 17 of their past 20 games (17-2-1), and seven of nine since Malkin returned Jan. 11. He scored in a 2-1 overtime loss to the Seattle Kraken on Thursday.
"I think Geno is getting better with every game that he plays," coach Mike Sullivan said. "He missed an awful lot of time. That's not an easy challenge for any player coming back into the lineup after missing as much time as he has. I give Geno so much credit for how hard he worked to get himself ready for that return-to-play process.
"Just the intensity of an NHL game is difficult to simulate. The only way you get that is by playing. … You can see the impact he has on our team, in particular offensively, with just his instincts."
Rust, 29, and Letang each said he was unconcerned with his contract status at training camp in September.
Rust, who missed 22 games because of injury, is fifth on the Penguins with 28 points (10 goals, 18 assists) in 21 games. He is the first-line right wing with Crosby, a center.
Letang is second with 38 points (five goals, 33 assists) in 39 games, behind forward Jake Guentzel (40). Letang has scored 18 points (four goals, 14 assists) in his past 13 games, including 15 points (two goals, 13 assists) during an NHL career-high, 10-game point streak from Jan. 2-21.
"He's a real competitive guy," Sullivan said Sunday. "His fitness level is off the charts. I think that's what has allowed Kris to continue to play at such a high level throughout the course of his career here, and most recently in particular."
