Would it be of significant advantage for a small business employer (3 ees) to age-weight his PS and MP plans to minimize the contributions to the non-key ees? What kind of testing is necessary besides 415© and 401(a)(4)?

Depending upon the goals of the business owner, this option may be appropriate. The plans would have to pass coverage testing. Additionally, the probability is that they would also be top heavy. In that instance, the minimum top heavy contribution requirement would have to be met.

Correct, but don't forget that top heavy testing might be on the basis of an aggregation group, in which case the T-H minimum might already be provided. Also, don't forget T-H vesting applies even if the contribution already meets the T-H requirements.

Whether someone should have an age-weighted plan depends on a lot of facts and circumstances, and we have virtually no facts. This is a topic that should be discussed with someone who understands the subject matter.

What is the age of the business owner relative to the employees? That's the first issue. Plan won't work real well if the owner is younger than the employees.

Age of the owner is 44 and he has 2 employees age 35 and 33. Owner makes over $200,000 other ees about $25,000 ea.

Thanks for your comments.

given the conditions you sighted, I come up with the following estimates:

age 44 owner 30,000
age 35 8.5% of pay
age 33 7.25% of pay
e.g. 7.25 * 1.085 * 1.085 = 8.5%
1.085 ^ 9 (9 year difference) = 2.08 and
2.08* 8.5 = 17.71% which is 30000/170000
(in an ideal world!)
it looks like you are close to squeezing out the full contribution and keeping within the 15% deductibility limit.
very close.
however, my calculations indicate an annual addition of 35,000 in the year 2001. this would blow the deductibility out of the water if you wanted maximixe the owner unless you did indeed have a money purchase plan.
Now, giving the owner 17.7% of pay and the rank and file 8.5 and 7.25, is it worth it? only you can decide.
note: these numbers may vary further if owner was born in the first half of the plan year and you use age definition nearest, but only if rank and file were born in secnd half of the year.

You probably already thought of this but is a PS/MP the right plan here? How much does the owner want to put away? Might a DB, 412(i), or tax deductible non qualified plan make more sense? Especially if he wants more than 30k.