At the last monthly meeting of the Prince George's Republican Club in Glenn Dale, club vice president R. Dan Ritchie made a point of urging the members to write to President Reagan to encourage him to seek reelection. But Fred Casey of Bowie, a retired Civil Service Commission investigator, stongly objected.

"I think the president has been listening to the wrong people," said Casey, who then launched into a stinging attack on Reagan's policies on federal workers and Social Security.

Not far from Casey sat Joe Parker, the schoolteacher who once came closer than any other black to defeating longtime state senator and power broker Tommie Broadwater. He was attending his first Republican Club meeting in many months.

Parker said later that he attended because a friend was the guest speaker. He said he had dropped out of party politics after concluding that the party "wanted blacks involved, but only to elect white candidates."

The feelings of Parker, who is discouraged by what he considers the party's lack of support for black candidates, and Casey, who is angry with the party right now because of Reagan's policies, reflect just some of the woes that today face the Prince George's Republicans.

Long outnumbered 3 to 1 by Democrats, the Republicans are in truly one of their darkest hours. Except for Marjorie Holt, who represents a portion of southern Prince George's in Congress, all other offices--from state senator to county executive to clerk of the court--are currently held by Democrats.

The one Republican who proved electable, Lawrence J. Hogan, former county executive and three-term congressman, says definitively that he has retired from politics.

Against this backdrop, county Republicans have launched a back-to-basics movement that they hope will result in a grassroots overhaul of their beleaguered party in time for the 1986 elections.

The first order of business, said Ritchie, a Riverdale businessman, is to build a precinct organization: in short, to start acting more like Democrats.

"Only a third of our 152 precincts have chairmen and not all of those chairmen are active," said Ritchie, one of the new movers and shakers in the party who decided to get involved after every Republican candidate was defeated in last year's local elections.

"We don't normally have sample ballots at the precincts. The Democrats will have five to ten people at a single precinct handing out sample ballots," he added.

To that end, the Republicans have scheduled for tomorrow the first of a series of "precinct organization meetings." Everyone who attends will receive a copy of "Tools of the Trade," a how-to guide on organizing the precincts. It covers such things as telephone canvassing, door-to-door campaigning, political advertising, and recruitment of volunteers.

The Republican Club, meanwhile, is conducting a massive mailing. About 500 letters recently went out and there are plans to reach all 50,707 registered Republicans by September, to ask them to become involved in local politics and contribute financially to the party.

Ritchie said that the mail drive has thus far resulted in committments of $25,000 for the party war chest.

The Republican Club also recently endorsed a candidate--John Ritchie, owner of a Laurel construction equipment firm--for election to the 5th Congressional District in 1986. No Republican has held that seat for nine years, since Hogan gave it up to run unsuccessfully for governor. The idea this time, the Republicans say, is to endorse someone early and get an early start at fund-raising.

Barbara Anderson, chairman of the Republican Central Committee, says the party wants to start recruiting qualified candidates now so that they will be able to run someone for each legislative and councilmanic seat, as well as for county executive.

The strategy during the last election, Anderson said, was not to "dig up" candidates, but to concentrate on helping a few individuals, such as Ella Ennis, former county liaison to the legislature, and former Hogan aide Wilbert Wilson, both of whom were well-qualifed and had some chance of winning.

"It didn't work," said Anderson.

But John Lally, an attorney and Democratic Party activist who was the chief aide to former county executive Winfield Kelly, says the Republicans can try all the new tactics they want, but "you've got to give people a reason to be a Republican in this county, and so far, they haven't come up with a good enough reason."

Republicans have, however, produced some good candidates, said State Sen. Howard A. Denis (R-Montgomery), but their problem has been the numbers. "Ella Ennis, for example, ran a textbook campaign," Denis said. "She did everything right but win."

Denis said he also thinks Republicans in both Montgomery and Prince George's are hurt by the fact that the gubernatorial and local elections do not take place in the same years as presidential elections. "The party has always been more successful in the national elections," Denis said.

The Democrats' supremacy in Prince George's, said Anderson, dates back to the Civil War days when many county residents identified with the conservative southern Democrats. Gradually, the county became more blue-collar and union-oriented and that, too, meant more votes for the Democratic Party.

Blacks represent 37 percent of the total county population, and a majority of them also vote Democratic.

Republican registration in the county has remained constant for the past 10 years, while the Democrats keeping making gains and now have 163,572 registered.

Few Republicans have changed registration over the years--as Fred Casey did last year, in a symbolic gesture to show his irritation with Reagan.

Instead, many county Republicans say their loyalty to the party stems more from a desire to safeguard the two-party system than any strong belief in Republican Party principles.

And that is why Joe Parker, disillusioned as he is, says he remains a Republican.