The biggest winner so far in the battle of the free agents between the Boston Celtics and New York Knicks is Rory Sparrow, who has a new guaranteed four-year, $2 million contract from the Knicks. He earned $90,000 last season.

That contract is far more than the Knicks would have paid for the three-year veteran guard from Villanova had the Celtics not signed Sparrow to an offer sheet. The Knicks, who feel that Sparrow is their second most valuable player after Bernard King, were forced to match the offer.

Sparrow was acquired midway through last season for forward Scott Hastings and $600,000. New York was 14-26 at the time of the trade, but with Sparrow as their point guard, they won 30 of their last 42 games. The Knicks beat the New Jersey Nets in the first round of the playoffs before being eliminated by the Philadelphia 76ers in four straight in the Eastern Conference semifinals.

The Celtics have also offered New York center Marvin Webster and forward Sly Williams guaranteed three-year, $1.35 million contracts.

The competition between the two teams started last week when the Knicks made a move toward signing Celtics free agent Kevin McHale. They reportedly offered him a guaranteed three-year contract calling for $3.5 million. McHale hasn't signed an offer sheet, however, and the Celtics have vowed to match any offer made to him.

Speculation is that the Celtics went after the Knicks' free agents to push the New York team payroll so high that the Knicks won't be permitted to sign McHale.

Under terms of the new collective-bargaining agreement that goes into effect next year, five teams had their payrolls frozen at this season's levels. The Knicks, with a reported team payroll of $5.5 million this season, are one of those teams, along with Los Angeles, Seattle, New Jersey and Philadelphia.

The NBA's other 18 teams will have no salary cap for the coming season, but will have one established for the 1984-85 season, based on their team payrolls at the end of the 1983-84 season.

In order for the Knicks to sign McHale, they would have to reduce the size of their payroll by whatever amount they pay him. Now that they have committed to paying Sparrow $500,000 a year, that would be difficult.

There is also a question of when they have to be at, or below, their cap. The Knicks say not until the beginning of next season, and the league says they can never exceed their cap.

Whether the Lakers keep free agent center Kareem Abdul-Jabbar should also be decided soon. The Chicago Bulls have reportedly offered him a guaranteed two-year contract for $2 million a year, and a meeting between Abdul-Jabbar's lawyer and Lakers owner Jerry Buss was scheduled for late yesterday in Los Angeles.

Abdul-Jabbar, 36, made $1 million last year and Buss is reportedly prepared to pay him $1.5 million for next season.