The move is part of a new round of mergers and acquisitions in the construction sector as firms bolt on extra services or increase their geographic coverage.
Sources close to WS Atkins said the firm had been in talks with Hanscomb for some months. It is understood the deal would be to buy the group's US arm, although an agreement has yet to be finalised.
Atkins chief executive Robin Southwell said the firm was in talks with a number of firms, but would not be drawn on which they were.
Southwell said: "There is a long list of firms, not just in the States but in the UK as well. We are in continual dialogue but I would not single out any firms in particular."
A source close to Atkins said a deal with Hanscomb, which has operations in the UK, Europe, Latin America and Asia as well as the USA, was imminent.
The source said: "There have been talks for at least two or three months. There are quite complicated ownership issues to be dealt with. The deal makes a lot of sense – the potential for Atkins to tie up in the States is huge."
Atkins has long harboured plans to expand its operation in the USA. Two years ago it bought Benham, a multidisciplinary consultant with headquarters in Oklahoma, for £32.3m.
Hanscomb, whose US arm is based in Atlanta, works mainly in markets such as aviation, car factories and infrastructure. Projects have included the construction of airport terminals in Texas, New York and San Francisco.
City sources said WS Atkins, Carillion and Interior Services Group were on the acquisition trail, especially in the facilities management market.
Alfred McAlpine's acquisition of facilities manager Stiell at the beginning of this month set the trend. One city boss said: "The Stiell deal has opened a lot of people's eyes. The market is very hot at the moment in terms of acquisitions."
One analyst said the deals were driven by corporate clients, who want to outsource more of their facilities. The analyst pointed to Balfour Beatty's acquisition of Yorkshire-based utility contractor Kenton this week as a sign of the growing trend.