Janus

, the nation's fastest-growing mutual fund firm, will soon launch a new growth fund,

Orion

, that appears to be similar to the $35.3 billion

(JAVLX)

Twenty fund that closed to new investors last April.

Ron Sachs, will run the new fund, which is slated for a June 30 launch, according to paperwork filed Friday with the

Securities and Exchange Commission

. A former attorney, Sachs joined Janus as an analyst in July 1996 and is co-manager of the $8.5 billion

(JAENX) - Get Report

Enterprise fund. The fund is up 138% over the past year, according to

Morningstar

.

Like Twenty, arguably the firm's most famous growth fund, Orion will be nondiversified, meaning Sachs can take big bets on relatively few stocks. It will hold about 20 stocks the manager thinks are poised for earnings growth and stock appreciation. Essentially, the fund will be an aggressive stock-picker's fund rather than a diversified core holding.

But there will be differences between the two funds. Partly due to its size, Twenty focuses primarily on large-cap stocks. Orion will follow more of an all-cap approach, potentially holding small-caps, according to the SEC filing and a Janus official. Like Twenty, the fund has leeway to invest 100% of its assets overseas, but it will probably only do so selectively.

Sachs is hardly a grizzled veteran, but that probably won't keep investors from throwing money at the fund. While he might be untested, Janus applies a similar growth style across its funds -- and that style has been hot for a couple of years. That has led to a tech bias and a whopping average 1999 return of more than 80% for its stock funds.

More than $9 billion went into Janus funds in January, roughly 50 cents of every dollar that went into domestic stock funds. The firm only has 15 stock funds, four of which are currently closed to new investors. Janus' reputation is so strong right now that the firm

raised more than $1 billion for its new

Strategic Value

fund in a four-week subscription period that ended Feb. 29, even though the value style is out of favor and considered by many to be beyond the firm's expertise.

The Orion fund's ability to play in small-caps might be hurt by a mountain of assets. Big funds often can't move nimbly among small-caps without moving their prices and reducing returns. A Janus spokeswoman said the firm has no asset target in mind.

The fund is sure to make a big splash this summer, not just because of Janus' reputation as a growth manager, but also because the firm's new funds have a reputation for racing out of the gate in their first year.