Part time before retirement

We are a small company under 100 employees and have several long time employess (20 + years)near or at retirement age. We would like to encourage them to work part-time instead of full time but do not know how to go about it without making them feel like they are being forced out or violating any age discrimination laws. Has anyone had success in doing this with their company or know of a company who has successfully handled this situation?
Comments
In your initial post, you said that these people were reaching retirement age, not that they were definitely planning to retire. If someone has not notified you of their intention to retire, I would not approach them about retiring, working part-time or anything related to that. If someone does notify you of their plan to retire, I think you could say that the company is making part-time employment available to pending retirees as a means of transition, strictly at their option.
Most experts on the psychological and social impact of retirement state that it's better for the individual to phase out rather than quit working abruptly, so this could be of benefit to them as well as you. A way to make it non-aversive (financially) to them would be to offer them the part-time option AFTER rather than before their intended retirement. I hope that makes sense.
We had an employee retire and then come back and work part-time. This spurred another employee who was near retirement to request reduced hours. Both situations worked out well.
Good luck!
Nae
Once they start questioning you about their retirement, then bring it up.
(You seem concerned about getting their job replacement trained and ready for their departure. However, if they don't provide you long term notice, what is the difference with any employee who just decides to "leave" for any reason.) Don't sweat this. It will work out with time.
E Wart