It's not famous yet, but Jackson Hewitt (JTAX) may soon be a roaring success. That's what money manager Roger Lipton expects, so he has been buying shares in the company, an up-and-coming H&R Block-type operation. It runs franchised offices that do computerized filing of tax returns.

So far, Jackson Hewitt, with just 1% of the market (vs. H&R's 12%) has been a winner: Shares shot from 9 in mid-June to 501/2 by Oct. 10. This week's plunge dropped it to 431/2. It closed at 433/4 on Oct. 29. But based on Jackson's fast growth, Lipton, who heads Lipton Financial Services, says the stock may hit 80 in 12 to 18 months.

Now No.2 in tax-preparation franchises, with 1,372 outlets in 41 states, Jackson Hewitt ''is a beneficiary of the new tax law,'' says analyst Cody McGarraugh of Scott & Stringfellow. Since Jackson focuses on the low to middle-income taxpayer, the new tax policy increasing the use of earned income tax credits as a way of easing the burden of low-wage earners boosts ''the level of urgency to expedite the tax refund process,'' the analyst explains. Jackson offers quick refunds through the use of electronic tax filing, as well as refund anticipation loans, which allow taxpayers to get a tax refund in three days to two weeks. The company is expected to add 400 new offices in the year ending April, 1998, and 500 more in fiscal 1999. H&R Block has more than 9,000 stores in operation.