My preference is to shuck the clams before smoking so they absorb more of the smoke flavor, but whole clams can be smoked until the shells open, about ten minutes. Fishmongers use different names for clams based on their size. The smallest harvestable clam is a littleneck (about one inch in diameter), then middleneck, followed by topneck. Larger clams are cherrystones (three to four per pound) and chowder clams. One pound of topneck clams contains about five to seven clams. From Mike Stines' article "How to Smoke Succulent Shellfish" here.
2 to 3 pounds littleneck or middleneck clams
Freshly minced parsley for garnish
Cocktail sauce, if desired
Soak the clams in cold water for an hour, which allows them to purge any sand. Scrub the clams under running cold water with a vegetable brush.
Shuck the clams. To shuck clams, you’ll need a clam knife (different from an oyster knife, as the tip is not curved and the blade is thinner) and a mesh glove to protect your hand if the knife slips. Experienced shuckers will just use a side towel to hold the clam. It’s easier to open clams if they have been chilled for several hours.
Hold the clam with the hinge facing the palm of your gloved hand. Using the side of the knife, wedge the blade between the shells at the front on the clam. When the shell opens, slide the knife around the clam to cut the adductor muscles holding the shells together. Run the knife along the top and bottom surfaces inside the knife to free the clam. Discard one half of the shell, reserving the other half for cooking and presentation.
Prepare the smoker for 225 degrees F. cooking using the wood of your choice (I recommend using maple or apple wood). Place the clams on a vegetable grate and smoke for 30 to 40 minutes.