No, they're not the Valacirca
According to the Index, included in the text from the second edition onwards, they represent the seven ships that carried the palantíri away from Númenor:
[The Seven stars of Elendil and his captains] originally represented the single stars on the banners of each of seven ships (of nine) that bore a palantír; in Gondor the seven stars were set about a white-flowered tree, over which the Kings set a winged crown.
Return of the King Index "Star, as emblem"
And boy is that a source I've never used before.
The design of the standard of Gondor
The only descriptions of the standard follow the following form:
There flowered a White Tree, and that was for Gondor; but Seven Stars were about it, and a high crown above it
Return of the King Book V Chapter 6: "The Battle of the Pelennor Fields
The precise arrangement of the stars is never described beyond this vague "set about." This doesn't appear to refer to a specific arrangement; the most relevant definitions of the word involve "near" and "on every side of", and there's no specific heraldric meaning to the word1.
A possibility for how Tolkien envisioned the Standard is given in the image below, which was submitted by him to his publishers as a possibly dust-jacket design for Return of the King:

Of course this isn't a perfect recreation of the description of the Standard, but is the only drawing of Tolkien's depicting anything similar to it; your mileage may vary.
The design used in the films likely takes its cue from another place we've seen seven stars: the Doors of Durin. Now, these aren't the same seven stars; per the Index, the stars of Durin probably are the Valacirca:
[The Stars of Durin] represented the Plough.
Return of the King Index "Star, as emblem"
"The Plough" is the UK name for what Americans call the Big Dipper, and what Tolkien called the Valacirca. Although I'm not sure of any textual evidence to support it, it seems likely that this is the intended meaning of the word.
Regardless, we're shown an image of the Doors of Durin, and the arrangement of the stars is similar to that seen on the film version of the Standard:

1 Thanks to Martha for confirming this