Feb 17 (Reuters) - Defense contractor Leidos Holdings LDOS.N reported fourth-quarter revenue below Wall Street estimates, as the six-week long U.S. government shutdown last year weighed on the firm's orders.

The shutdown, the longest in the country's history, ended in November after severely disrupting government operations and weighing on contractors such as Leidos, which provides IT, weapons and other services to federal agencies.

Shares of Leidos, which also supplies air traffic control systems to the Federal Aviation Administration, fell 1.6% in premarket trading.

Last month, defense supplier L3Harris Technologies LHX.N also flagged a hit from the shutdown, largely in its space systems business.

Leidos' revenue during the fourth quarter came in at $4.21 billion, down 3.6% from last year, and lower than analysts' estimates of $4.31 billion, according to data compiled by LSEG.

Results also took a hit from a 9.3% drop in sales in its health and civil segment, which provides electronic health record systems to both the Department of Defense and Veteran Affairs hospitals.

On an adjusted basis, however, the Reston, Virginia-based company's fourth-quarter profit per share of $2.76 beat expectations of $2.61, helped by a 160-basis point expansion in its adjusted core profit margin and increased cost controls.

Leidos forecast 2026 adjusted profit between $12.05 and $12.45 per share, the midpoint of which is 4 cents lower than analysts' estimates of $12.29.

(Reporting by Aishwarya Jain in Bengaluru; Editing by Devika Syamnath)

((Aishwarya.Jain@thomsonreuters.com;))