Probably not without a trade-off in other respects - sometimes smoothing helps (particularly in sky areas) but this will reduce the apparent sharpeness of other areas.
The question is why are you getting problem grain in the first place? Even 400 ASA (with decent film!) - if properly exposed should not produce offensive grain. Grain is usually only a problem if the image is underexposed.
If you have an even slightly underexpsoed image and you try and compensate during scanning, you will increase the problem. Instead, try making the initial scan true to the original (ie. slightly underexposed) and then adjusting the scanned image using "tone curve" in photoshop.
Another trick which might work - scan the image at a high resolution (much higher than required) and then in photoshop resample the image down to the required size, followed by application of unsharp mask.
Colin K. Work, Pixstel