Eliot Robertson, the assistant superintendent for budget at the Prince George's County schools, appeared before four groups of school employes in three days last week attacking what he described as the budget "blackmail" and "falsehoods" of County Executive Lawrence J. Hogan.

At the same time, Hogan, members of his staff, and at least one member of the staff of the county budget office were going to meetings around the county to defend the county executive and argue for the need to cut the school board's proposed budget. A letter on county stationery mailed from Hogan's office to businessmen with county funds carried the same message.

The school board staff and Hogan's office thus joined in what has become a bitter and well-financed struggled of a wide range of special interests over the county's 1980 proposed budget.

Of course, the battle takes place, in one form or another, every year. It pits the money-takers-including the school board, county employes, and community groups that benefit from county services-against the money manager, the county executive, and taxpayers who want to cut spending.

In the middle is the county council, the final judge of how much money is spent and for what . In the past, council members say, the campaigns by the special interests-particularly by those on the receiving end of county funds-have had a significant influence on the council's budget deliberations.

And this year, with funding for county services spread thin because of a voter-approved limit on county tax revenues, the speci interest groups are working harder than ever.

According to Toby Rich, the president of the Prince George's County Educators Association, the 7,000-member teachers' union has raised more than $3,500 to pay for its budget lobbying. A coalition of 10 county unions, including the teachers, has raised thousands of dollars more to help with the fight.

"We're on the campaign trail, just like the council members were last fall," said Rich. "The campaign is to get the total education budget funded."

In particular, the teachers and other unions are interested in persuading the council to fund cost-of-living increase of 5 percent for county employes, rather than the 3 percent included in Hogan's proposed budget.

By marshaling thousands of their members at the council's budget hearings, running radio and newspaper advertisements, organizing marches and letter-writing campaigns, and personally lobbying council members, the unions hope to force their point of view upon the council.

They are not the only interest groups campaigning, however. Members of the school board-and the professional staff that works for them-have also been touring the county to raise support for the school board's proposed budget. The school staff also has used county money to print studies showing how Hogan's cuts in the school budget will harm the schools.

Meanwhile, Hogan and the school board have gone to battle as if they themselves were special interest groups, spending money, campaigning and lobbying in an effort to bring pressure to bear on the council to keep the budget as tight as possible.

Although council members say they always base their budget votes on serious consideration of the needs of various county agencies and services, they concede that the pressure has its effect.

"Nothing is done purely because of political tactics," said council member Gerard T. McDonough. "And nothing is totally because of merit.It's always a mixture."

The mixture results in part, council members say, because of the political power held by the special interests. Rich and council members estimate that the teachers' union alone can swing 12,000 to 15,000 votes in a county-wide election.

In 1974, aides to former county executive Winfield M. Kelly Jr. said the vehement opposition of the teachers' union to the cuts in the school budget proposed by then-Executive William W. Gullett provided Kelly's margin of victory over Gullett.

In addition to the special interests' political power, the psychological pressure they create through colorful demonstrations at the council's public hearings on the budget has some effect.

As in the past, thousands of persons-most of them from unions or other interest groups-descended on the concil's first public hearing last week armed with banners, placards and ringing speeches, all of which were recorded by the assembled television cameras and press.

Hogan urged businessmen who received his budget letter to turn out at the public hearings and speak for his proposed budget, and urged that his supporters arrive "before the special-interests pack the room."

"If they just got up there and recited facts, it might be different," said one council member, "but with all that show in front of the media, some coucil members can be intimidated."

One example of the intimidation, council members said, can be found in the history of county grants to non-profit community groups. For the past several years, including this year, the grants-most of them relatively small-to nonprofit groups serving the deaf, the handicapped or the economically disadvantaged have been reduced or elminated from the budget by the county executive.

After large, sometimes emotional demonstrations at public hearings, the council has always restored the grants to groups such as the Washington Ear and Family Services of Prince George's.

"You can make a good argument that some of these grants are not as important as some of the other county services" explained a council member. "But face it, you just can't stomp on handicapped people. It's not politically acceptable."

There is one council member, Ann Lombardi, who says that the demonstrations by interest groups this year have had little effect so far on her thoughts. Special interest pressure is "not effective on me," she said.

But, Lombardi added, "I'm probably going to be a one-term council member because of that attitude."