The Fairfax County Board of Supervisors yesterday approved the first phase of a $3.8 million program that police say will improve law enforcement in the county by using helicopters for traffic control and medical emergencies and plugging into a regional automated fingerprint identification network.

The board also voted to accept tentatively a staff proposal limiting teacher and county-employe pay raises to 3 percent next year, citing predictions of lean revenues. County officials said the pay increase for approximately 17,000 public employees will cost $15.3 million.

Alhough supervisors are weeks away from receiving a proposed fiscal 1983 budget from the county staff, the board voted to guarantee the police department $887,700 in the first year of a three-year program to improve technology and add 20 new workers. Board approval will be required for the next two years to complete the program.

"This will mean some sweeping changes in the way police protection will be provided in the county," said board member Marie B. Travesky. "We have been doing a lot of it in an archaic fashion."

Police Chief Carroll D. Buracker's plan for upgrading the department -- the first major changes he has proposed to the board since taking his job about a year ago -- calls for two helicopters equipped with sophisticated equipment, including infrared lights that can "see" through trees and fog and heat-sensitive devices for locating bodies in heavily wooded areas.

The helicopters would be used mostly for traffic control. Buracker said police will monitor the county's busiest highways from the helicopters, dispatching motorcycle patrolmen to help alleviate bottlenecks and traffic jams.

The three-year costs of leasing the helicopters, salaries for five pilots and five cardiac care technicians and maintenance costs will be about $1.5 million, police said. The board approved spending $378,865 in fiscal 1983 to begin training pilots and crew and make initial arrangements for leasing equipment next year.

The board also approved first-year funding for:

* $63,117 to launch an auxiliary police force that eventually would be composed of 100 civilians with limited police powers and assigned to help police with traffic control, school crossings, hospital guard services and clerical work.

* Merging most of the county's park police service with the police department, upgrading the pay scales of officers from the park police service and expanding their duties.

Also included in the three-year program is a plan for Fairfax to join an automated fingerprint identification network to replace the cumbersome manual system now in use. The automated system is now used by police in Montgomery and Prince George's counties and has been funded in the District. It would cost Fairfax $870,400. Funding would not begin until fiscal 1984.

The board voted 8-1 to approve the special police improvements budget, with Supervisor James M. Scott casting the only dissenting vote.

"I don't recall we have ever approved such a large amount of funds in such a short time outside the budget process," Scott said. "We need to compare it to our other priorties."