"The following are examples of works not subject to copyright and applications for registration of such works cannot be entertained: (...) typeface as typeface" 37 CFR 202.1(e).
House of Representatives report accompanied the new copyright law when passed in 1976: "The Committee has considered, but chosen to defer, the possibility of protecting the design of typefaces. A 'typeface' can be defined as a set of letters, numbers, or other symbolic characters, whose forms are related by repeating design elements consistently applied in a notational system and are intended to be embodied in articles whose intrinsic utilitarian function is for use in composing text or other cognizable combinations of characters. The Committee does not regard the design of typeface, as thus defined, to be a copyrightable 'pictorial, graphic, or sculptural work' within the meaning of this bill and the application of the dividing line in section 101." H.R. Rep. No. 94-1476, 94th Congress, 2d Session at 55 (1976), reprinted in1978 U.S. Cong. and Admin. News 5659, 5668.

It's also in accordance with a court case that has considered the matter: Eltra Corp. V. Ringer, 579 F.2d 294, 208 USPQ 1 (1978, C.A. 4, Va.).

The U.S. Copyright Office holds that a bitmapped font is nothing more than a computerized representation of a typeface, and as such is not copyrightable:

"The [September 29, 1988] Policy Decision [published at 53 FR 38110] based on the [October 10,] 1986 Notice of Inquiry [published at 51 FR 36410] reiterated a number of previous registration decisions made by the [Copyright] Office. First, under existing law, typeface as such is not registerable. The Policy Decision then went on to state the Office's position that 'data that merely represents an electronic depiction of a particular typeface or individual letterform' [that is, a bitmapped font] is also not registerable." 57 FR 6201.