The state Department of Transportation plans to launch a hiring push in preparation for a slew of maintenance and modernization projects teed up by a new federal infrastructure law, but officials find themselves grappling with a tricky labor challenge.

Unlike many other industries where total employment dropped during the COVID-19 pandemic, the number of workers in scientific and construction fields – which are most important to the projects MassDOT hopes to accomplish – increased about 2.5 percent each over the past two years, according to data presented by MassDOT Chief Human Resources Officer Matthew Knosp.

“Those markets actually grew over the last couple of years. This means that overall, some of the candidate pools for many of our engineering and construction positions have become smaller compared to the pools we’re seeing for other sectors,” Knosp said at an audit and finance committee meeting Wednesday.

Massachusetts expects to receive about $9.5 billion in formula funding over the next five-plus years as part of the bipartisan infrastructure law, and state officials say they hope to capitalize on even more money that is available through competitive grant programs.

Gov. Charlie Baker last month filed a $9.7 billion bond bill to help put those dollars to work and catalyze projects to repair highways and bridges, modernize MBTA infrastructure and vehicles, build out the T’s electric bus infrastructure and more.

MassDOT had about 3,500 full-time equivalent employees at the end of the fiscal year 2021. Since then, the department has added 122 workers and shed 72 due to attrition, according to a presentation Knosp delivered Wednesday.

The department hopes to hire 81 more workers over the final weeks of the fiscal year 2022 and another 160 in the fiscal year 2023 to help complete infrastructure law-backed projects, the presentation said. That would bump up MassDOT’s headcount to nearly 300 more FTEs than at the end of FY21.

“We’re looking at this as both a need for a short-term staff-up to deliver on those programs but also a long-term increase in hiring as we look at both the amount of attrition that would come from having a larger staff and one of the things we’ve talked about in the past: we are keenly aware that we have some retirement waves coming,” Knosp said.

Knosp told transportation overseers that MassDOT employees have been heading for the exits at a higher rate over the past two years, though he stressed the department’s attrition rate remains low compared to other employers.

Amid the hiring push, it will be “equally if not more important” for MassDOT to focus on retaining experienced staff, Knosp said.

“We have a lot of key staff who will need to be working closely with our hiring managers to ensure we’re hiring to replace but also training and developing our current workforce to be able to grow into some of those positions as well,” he said. “It’s a big challenge, but I think it’s one we feel we’re well-positioned for.”