Keast has been promoted to director of rugby at Harlequins as the London club introduce a southern hemisphere-style coaching system. He coached Quins to third place in the league and to the Pilkington Cup semi-final last season. Cusworth takes the same job title at Worcester.
Keast will be responsible for all coaching and playing matters at The Stoop, while contractual and financial arrangements will be left to the chief executive, Donald Kerr.
Keast's promotion backroom comes as Quins attempt to "streamline" club business in the wake of Dick Best's sudden departure at the end of last season. Best, a former England coach, was sacked by Quins only two years into a 10-year rolling contract after discontent surfaced among the playing squad about training schedules.
Keast said: "I hope I can fill the void left by Dick Best's departure. Dividing the squad management responsibilities in this way is designed to enable the director of rugby to concentrate his efforts on playing and coaching whilst ensuring that the business management of the squad continues on a sound footing.
"Many clubs in the southern hemisphere have found such a system to be beneficial to both players and the club. It is important that we streamline the club to keep up with the modern game."
Meanwhile, Malcolm Wall has succeeded Roger Looker as chairman at The Stoop. The 40-year-old former Quins lock is the deputy director of United Broadcasting and Entertainment, which owns the ITV companies Anglia, Meridian and HTV.
The appointment of Cusworth, who has just returned from England's one- off Test with Australia in Sydney, is a major coup for Worcester. He will sign today with last season's Courage Division Four champions after several meetings with Worcester's multi-millionaire backer, Cecil Duckworth.
Mike Robins, the club chairman, said: "We are starting to attract top- class players and you must get the best coach for them. They don't come much better than Les.
"He did not take much persuading to come here. The England job is part- time and, if the terms were right, I think he was looking to get involved in the game at club level. This role appealed to him."
Worcester had also been in negotiations with the former England full- back Jonathan Callard for the post but his club, Bath, refused to release the player from his contract.
Worcester will be happy to allow Cusworth to continue as Jack Rowell's No 2 if he is re-appointed by England.
Robins said: "He did say when we made the offer if we would be prepared to let him carry on with England and we were more than happy to say 'yes'. It would give great kudos to the club."
Cusworth, who will meet the Worcester players for the first time at this evening's training session, began his rugby career with Wakefield before joining Moseley. He then moved to Leicester whence he gained a dozen England caps.Reuse content