Tensions in the Teamsters strike against the area's largest concrete supplier, Virginia Concrete Co., escalated sharply yesterday as the company brought in 100 drivers from Florida and Georgia to begin manning concrete trucks.

Officials from Teamsters Local 639 said the move violates a federal law "prohibiting the importation of strikebreakers" and complained to the U.S. attorney's office in Alexandria and the FBI.

"Any time a company brings in scabs and goons, it's going to increase tensions," said union local president Philip Feaster.

"The use of temporary replacements in no way violates federal law ," said Tom Wotring, an attorney representing Virginia Concrete in its labor negotiations.

"We did this to service our customers, pure and simple."

The workers are employes of Florida Rock Industries, a Florida-based company that owns Virginia Concrete Co. Wotring said they were "only temporary replacements."

The presence of police also increased yesterday at the company's main Springfield plant. About three dozen Fairfax County police officers equipped with riot gear lined the roads into the plant and stood at the entrances.

Police said the sharp jump in the number of officers was in response to the number of trucks rolling out of the plant and to threats against the trucks.

Two picketers were struck and slightly injured by a concrete truck and one man, a laid-off construction worker, was arrested.

Although the level of rhetoric and tension appeared to escalate, union officials said there was only a single issue keeping them from accepting the package offered by Virginia Concrete last week -- the expiration date of the next contract.

In what it termed its "final offer," the company agreed to a 15 percent wage increase over three years, but insisted that the contract last only 30 months, expiring in November instead of May.

Union officials insist on a May expiration date because of the leverage a spring date provides compared to winter, when construction work is slow.

Both union and company officials said they were "willing to talk," although no talks were scheduled.

Virginia Concrete put more trucks and plants on line yesterday than at any time since the strike began on May 16, rolling 65 of 200 mixers out of three of 11 area plants.

The strike, which entered its third week yesterday, has taken the wind out of a construction boom in Northern Virginia, with scores of building projects delayed and workers laid off because construction managers cannot get concrete.

At the company's Springfield plant, the trucks had to run a gauntlet of angry, shouting picketers. Accounts of the incident in which the two men were hit varied. The union said the trucks did not slow to allow picketers to move out of the way. Police said the men refused to move as required by law.

The man who was arrested, Charles E. Hinders, 18, of McLean, was charged with obstructing free passage of vehicles and released on his own recognizance.

The striking drivers were joined on the picket line yesterday by a striking United Airlines pilot, Kevin Dillon, who came to show his solidarity with what he said were fellow operators of large vehicles.