Northern Virginia teachers groups and school officials said yesterday that the Robb administration's plans for merit pay increases for master teachers will cause an uproar among the state's 65,000 rank and file teachers unless they get a general salary increase first.

State Secretary of Education John T. Casteen's announcement Monday of a possible pilot project on merit pay came within days after Robb proposed spending $250 million to raise the salaries of public school teachers and university faculty over the next two budget years.

However, many area teachers and their representatives say they fear that local officials will use increases in state funding to schools for areas other than salaries--a pattern they say school administrators have followed in previous years.

If merit pay is approved "things will get much worse than they are now," said Paul Moran, president of the Arlington Education Association. Teachers in Arlington are already upset about the results of a new evaluation system by principals that many teachers fear may eventually be used to determine who gets merit pay increases.

In Alexandria, where morale is low among teachers angered by this year's 3 percent cost of living increases, Superintendent Robert Peebles said institutingmerit pay without across-the-board salary increases is "a dangerous thing to do."

The $500,000 pilot project for merit pay raises and other incentives for master teachers in Virginia would give $1,000 cash payments to teachers deemed superior--much like the "master teacher" determinations at the cornerstone of President Reagan's plans for improving education. The teachers could also receive $2,500 "master fellowships." The pilot project which would be tested in one to three school districts involving 100 to 200 teachers.

Teachers nationwide generally oppose merit pay systems because "it doesn't address the general problem of teachers' compensation," according to Allan Caudill, president of the Education Association of Alexandria. "We've got to have adequate teacher pay before we get to merit pay."

In Prince William County, education association director Joy Arnold agreed with Caudill's criticism of merit pay proposals. "The fundamental error in the sudden promulgation of all the merit pay plans is you've got to first of all be paying people a legitimate salary," Arnold said yesterday.

In Fairfax County, school board members are considering hiring a consultant to study merit pay, according to school spokesman George Hamel. "The feeling is that it all sounds very good but there are so many different things to iron out that our board is not jumping into it, but is considering it," he said.

In Arlington, a county board-appointed task force is studying a merit pay plan for county employes. In Alexandria, school officials this fall will consider a "reward and incentive" plan for teachers, according to Peebles.

The Prince Georges' County school system is implementing a plan involving the master teacher concept similar to the pilot project proposed by Robb. Each of the county's 20 high schools will have four "teacher coordinators," experts in their fields of study, who will work with their colleagues on improving their teaching skills on a daily basis beginning next year. They will receive extra pay, a school spokesman said.

In the District, congressional leaders have said either Congress or the District Board of Education should begin studying merit pay. No such programs exist in Montgomery or Prince William counties.

Much of the controversy over merit pay is about the way outstanding or superior teachers would be determined. "In sales there's a bottom line: How many sales did you make?" said Caudill. "In education, there's no objective measure."

Teachers in Arlington have complained that their recent evaluations by their school principals were based on such factors as attendance at faculty social events and an administrator's "gut feeling."

In any case, Arlington Education Association president Moran says he doubts merit pay is the way to motivate teachers. "I don't think teachers need to have a carrot out in front of them to work," he said.