Prince George's County police began a work slowdown yesterday, enforcing the law "only when the public or a police officer was endangered," according to the president of the county's police union.

The effectiveness of the slowdown was hard to measure precisely. Police union president Laney Hester claimed that 95 to 98 percent of his men were participating in it. Officers were spotted honking and waving at speeding motorists and sticking their radar guns up toward the sky.

The police protest comes at a time of extremely anxiety within the department. The police rank-and-file is upset not only by the fact that contract negotiations between the officers and the county administration have broken off but also by the fatal shootings of two county policemen in Hyattsville Monday morning. The police blame Chief John W. Rhoads for not giving them moral or financial support and gave the chief a vote of no confidence at a meeting Thursday before the slowdown began.

Chief Rhoads, apparently shaken by the unanimous "no confidence" vote said he "would consider resigning if I got the feeling that (I am) what this is all about."

Rhoads later qualified this statement by saying that any resignation would be at least a couple of weeks down the road and he did not feel that he is actually the issue.

About 125 officers, many of them with their wives and children showed up at the County Administration Building at 8:30 a.m. to protest the county's handling of the stalled contract negotiations. Virtually all them wore T-shirts which said "Treat Us Right," on the front and "No Tickey, No Washey," on the back.

Peter F. Morgan, whose firing on June 21 for shooting a fleeing shop-lifting suspect contributed to the angry mood of the officers, joined with the marchers wearing a paper bag over his head to symbolize his status as no longer a member of the force.

The union leadership's plan to force the county to meet the officers' demands, according to informed sources, is to do nothing illegal. Officers have been urged to enforce the law if directly ordered to do so by superiors, to avoid confrontation and to make themselves visible and available ot citizens. "We'll respond to calls right away," one union board member said. "And if there's a larceny, or a holdup or a street robbery we'll take a report, of course. But don't count on us making any arrests."

Union vice president Tom Lennon said the policemen believed the county was trying to force into an illegal strike so they could be ordered back on the job. "We won't do that though," he said."They'll never be able to say we've called a strike or we're not working. We are working. Our guys are reporting in.But that's all."

Hester announced that his organization, the Fraternal Order of Police, had received a letter from the county's Public Employees Relations Board ordering the union and the county to submit to binding arbitration, pending approval of that order by the County Council.

County Executive Winfield M. Kelly Jr., who called a news conference as soon as Hester's ended, said he had no intention of submitting to binding arbitration.

"I will not put this county's financial matters in the hands of outsiders," he said. "We are determined to keep the tax rate down both now and in the future. We've worked hard for that and we won't give that up to decisions made by people outside the county. The place to solve this is at the bargaining table."

Kelly also expressed confidence in Rhoads, calling him "one of the finest chiefs in this country. This is a difficult time for him as it is for all of us," he added. "But we've been through tough times before."

After receiving the letter from the Public Employees Relations Board shortly after noon, Hester requested a meeting with members of the County Council, who have the power under the county's labor code to approve an order by the independent employe relations board for binding arbitration.

By 4 p.m., the scheduled time for the meeting, about 250 policemen along with wives and children, totalling about 350 to 400 people, were jammed into the council's 224-seat hearing room.

At 4:15 p.m. eight of the 11 council members, led by Chairman Francis W. White, arrived to meet with them. Hester, in a voice that was hoarse from Thursday's meeting, asked the council to call a special meeting to consider approving the employe relations board's letter.

"I urge you to act on this as soon as possible," Hester said. "We are all at the end of our ropes. We are willing to accept any decision made by an arbitration board without question. Anything to get a settlement."

White told Hester and the others in the room that, "I can assure you we will deal with this matter expeditously." This satisfied the policemen , who left moments later, after loudly agreeing to "stick together as long as necessary even if it takes years," in the words of Tom Lennon.

After the meeting White said he had no intention as of now of calling a special meeting. "I think the absolute earliest we will act on this is Wednesday," he said. (Wednesday is the council's next scheduled legislative session.) "We have to give the letter to our staff so they can determine what our role in this is. This is the first time we have been faced with this situation."

Councilman Francis B. Francois said he was not sure the council could take any action since it had not officially been contacted by the employe relations board.

Hester said he was not surprised that the council would not take action until Wednesday. "I was afraid they might say 30 days," he said. He added that currently there were no plans to return to negotiations although earlier in the day Kelly had said the county would be willing to return to the negotiation table.

Behind the scenes, sources said. Rhoads continued to attempt to mediate a settlement as he has been doing since talks first broke down Wednesday morning.

The two groups appear close to a settlement. The county has offered the union members the right to retire after 20 years with a pension of 46 per cent of their final salary, a figure Hester's group is willing to accept. Currently county poicemen retire after 25 years with a 50 percent pension.

In return for the 20-year retirement, however, the county has asked the police to limit the raises officers joining the force after 1978 can receive without getting promoted.