I am trying to calculate the necessary sample size for a 2x2 factorial design. I have two questions.

1) I am using the package pwr and the one way anova function to calculate the necessary sample size using the following code

pwr.anova.test(k = , n = , f = , sig.level = , power = )

However, I would like to look at two way anova, since this is more efficient at estimating group means than one way anova. There is no two-way anova function that I could find. Is there a package or routine in [R] to do this?

2) Moreover, am I safe in assuming that since I am using a one-way anova power calculations, that the sample size will be more conservative (i.e. larger)?