The vacillating Nasdaq Stock Market last week reclaimed some of the territory scored by several of last year's best performing stocks and then arbitrarily bestowed big gains on some long-struggling little companies.

The week's big winner was Infodata Systems Inc. of Fairfax, the stock of which jumped to $5.50 a share from $2 after the software company said it had agreed to make an investment in Redknife, a small Silicon Valley company working on computer systems for electronic commerce.

The announcement of Infodata's investment of an undisclosed amount in Redknife set off a three-day trading frenzy that drove Infodata stock to its highest level in almost two years. Ordinarily fewer than 100,000 shares of Infodata are traded daily, but Wednesday the volume jumped to 850,000 and the price rose to $3.68 3/4 after starting the week at less than $2. The stock lost a few cents a share as volume swelled to 1.7 million Thursday, but the next day the trading exploded to more than 3 million shares, pushing the stock past $5 for the first time since the spring of 1998.

Another unexpected winner in the erratic week on Wall Street was U.S. Office Products Co., the stock of which soared after the company announced that it had sold a 60 percent stake in a technology company it owns in New Zealand. The transaction gave long-struggling U.S. Office Products $53 million to pay down its debt, which should produce a big savings in interest costs.

The week's leading loser was Hanger Orthopedic Group Inc. of Bethesda. Its stock lost more than half its value after the company warned that it would only break even for the fourth quarter of the year instead of earning the profit of 25 cents a share that analysts had predicted. Hanger Orthopedic, the nation's biggest maker and fitter of artificial limbs, blamed the shortfall on NovaCare Inc., which it acquired last year.

The Washington Post-Bloomberg regional stock index hit an all-time high of 185.19 last Monday before the market started to wobble. The value of the index kept sinking Tuesday, to 177.23, though it came back slightly through the week to recover three points, ending the week at 182.81, a loss of 1.2 percent.