Swiss banks, feminism, John Dean, more; Safety in Numbers, by Nicholas Faith. New York: The Viking Press. 368 pp. $15. 95.

According to popular belief, the secrecy laws surrounding Swiss banking were enacted to protect the savings of German Jews from Nazi investigators before World War II.

According to Nicholas Faith, however, the Swiss actually adopted their secrecy provisions from less altruistic motives - to foil attempts by France to track down wealthy French tax evaders holding illicit Swiss accounts.

In ''Safety in Numbers,'' Mr. Faith, a British journalist, tunnels deep into the subterranean financial world of the mysterious ''Gnomes of Zurich.'' He skillfully uses facts and figures to debunk some cherished myths while documenting others.

For example, Faith points out that despite their image of fiscal stability, Swiss bankers often play fast and loose - more than half of the 1,200 or so banks established in Switzerland since the 18th century have failed. But he supports the conception that ''the evasion of domestic laws and taxes forms probably the single most substantial feature common to Swiss banking clients.''

Notoriously familiar names - fugitive financier Robert Vesco, author-turned-con-artist Clifford Irving, reputed mob chief Meyer Lansky - pop up with regularity. Special attention is given to efforts made by US law officials in the 1970s to penetrate Swiss banking secrecy.

It all amounts to a crash course in cutthroat international finance, where intricate schemes, such as the ''three-cornered window-dressing loan,'' are commonplace. For readers who find romance in big money, the $400 billion or so stashed away in Switzerland makes a swashbuckling central figure.