Kudos for trying to want the best of both worlds, but it is tough. I too enjoy competing in sprint triathlons and other short endurance races. I recently did the Chicago Urbanathlon and a half marathon. Now my offseason is here and I plan on getting my strength numbers back up again.
You did not provide any information like where you are located (cold/snowy winters would make a difference in your conditioning programming), how old you are, what your recovery is like, and what is your prior experience with strength training. People much smarter than me and with much more experience can chime in, but I'll give it a go.
Your endurance and strength will cycle in waves, so take the opportunity this offseason to boost your strength so you are ready for the rigors of your upcoming season. Limit your swim/bike/run to maybe one session of each discipline each week. Be sure to cap your intensity on those sessions so as not to hurt your strength progress. Maintain your base only. If possible, drop the rowing (unless of course you are in an area where there is a lot of snow and running outside is not an option).
As far as lifting goes, a good 3x a week program I completed was the following:
Snatch - up to max for the day, 10-12 singles
Snatch Pull - 3x3
Front Squat - 5x3
OH Squat or Snatch Balance - 5x3
Push Press or Snatch Push Press - 5x5
RDL - 3x5
Clean & Jerk - up to max for the day, 8-10 singles
Clean Pull - 3x3
Back Squat - 5x5
Obviously you would want to do these on non-consecutive days. So you could alternate lifting days with conditioning days.
Hope this helps. Good luck.