In a large pot of boiling salted water, cook fettuccine according to package instructions. Add asparagus for last 2 minutes of cooking time. Drain, reserving 1 1/2 cups cooking water. Return pasta and asparagus to pot.
Meanwhile, in large non-stick skillet, heat oil over medium heat. Add leeks and cook until tender, 8 - 10 minutes.
Add reserved pasta water, cream cheese, tarragon, and chives, and stir until cream cheese is melted. Pour over pasta, ad smoke salmon and toss until well combined. Season with salt and pepper to taste.