Despite the strongest insurgent movement in eight years and the apparent unpopularity of County Executive. Winfield M. Kelly Jr., the entrenched Prince George's Democratic organization is expected this month to nearly duplicate its 1974 primary election sweep of all but three races in the county.

The Democrats '78 slate, bolstered by a campaign treasury of more than $200,000 and a party discipline unmatched in Maryland politics, appears in danger of losing at most seven of the more than 60 contests in the Sept. 12 primary, according to a district-by-district survey of the county's maverick and regular Democrats.

In addition, the organization is expected to provide the ticket of Acting Gov. Blair Lee III and Steny Hoyer with a substantial majority of the county's vote in the Democratic gubernatorial primary, perhaps as much as 65 per cent. Prince George's Hoyer's home base, is the only county in the state that the three other Democratic candidates for governor have conceded to Lee.

"The Hoyer machine is too strong there," said an aide to Baltimore county Executive Theodore G. Venetoulis, who is considered Lee's strongest challenger. "We think we have a reasonable chance of carrying every other county, but it would be asking too much to carry Prince George's. The question there is simply how many people are going to vote."

Prince George's traditionally has had one of the lowest voter turnout percentages in the state - between 25 and 35 per cent in past primaries. Although the low turnouts have never hurt the county organization, whose vote is reliable if small, it could lessen the impact of the heavy Lee vote in a statewide election.

The county organization, which began its 1978 election preparations with the expectation that Hoyer would be running for governor (he dropped out in early June to join Lee's ticket), spent several months registering new voters and refining its get-out-the-vote techniques to make the county vote more important on the state level. One result of that effort is that the county's registration has jumped from 2 to 1 to 3 to 1 Democratic since 1974. The other result will not be known until election day.

"We're pushing for a 40 percent turnout," said John McDonough, an aide to Kelly who is serving as the campaign manager for the Democrats '78 slate. "If we can get more than 60,000 people out "there are about 155,000 registered Democrats in the countryl, then the vote for Lee-Hoyer will have a statewide impact."

While Venetoulis and the two other Democratic candidates for governor, Harry R. Hughes and Walter S. Orlinsky, have had to build organizations from scratch in Prime George's, the Lee Campaign has relied exclusively on the county's regular slate. All of the slate's brochares and sample ballots list Lee and Hoyer at the top, and the voter identification surveys that the slate has been conducting for the past two months have included questions about Lee.

Although Venetoulis and Hughes, whose running mate, Samuel W. Bogley, is a county councilman from the Bowie area, have been endorsed by several independent Democratic candidates in the county, the local and statewide campaign efforts have been run separately.

The inability or reluctance of the insurgent Democrats seeking General Assembly, County Council and courthouse positions to band together in their attempts to displace the party regulars is one of the major reasons they are expected to make minimal gains in the county primary.

"Running against the slate is like guerrilla warfare," said Tom Mooney, a maverick delegate candidate in the Hyattswille-based 23rd District.

Mooney and another independent delegate candidate in the 23rd, Anthony Cieoris, ate among the handful of insurgents considered to have a realistic chance of succeeding in their guerrilla warfare against the organization's heavy artillery.

The other insurgents in that category include delegate candidates James Forsythe and Tim Maloney in the Laurel-based 21st; Senate candidate William Goodman and delegate hopeful David Bird in the New Carrollton-based 23rd; Del. Lee Green, who is challenging incumbent Edward Conroy for the Senate seat in the Bowie area; Del. Decatur Trotter, who is challenging Sen. Tommie Broadwater in the predominantly-black 25th; Councilman Francis White, running againt the slate for a delegate seat in the District Heights area; and Sue V. Mills, the outspoken cousty school board member who is seeking an at-large position on the county council.

Even these formidable independents recognize the advantages their slate opponents have.

The slate has enough money to print 300,000 brochures and enough volunteers to distribute them to every registered Democrat in the county.

It also has enough money to print up nearly 800,000 sample ballots and make sure that every voter gets one before the election and again on election day. The sample ballots are considered one of the most important factors in the low-visibility races for council and courthouse positions.

The maverick Democrats also have been hampered by a lack of eye-catching issues in campaign. An attempt to center the opposition around a Proposition-13 style referendum was cut short when County executive Kelly, the leader of the organization, endorsed it.

Attempts to characterize the organization as a monolithic machine apparently have not caught on with the voters.

"I don't think anyone's listening to that stuff anymore," said Gerard Devlin, a slate delegate from Bowie. "We've gone through a cycle in politics where outsiders like Jimmy Carter could run against the establishment. But now I think people are more interested in technical competence than enthusiasm. That's been hurting the outsiders here, I think."

Insurgent Mooney, who has visited every door in his district over the past eight months, admitted that "only a handful of people" raised the machine as an issue.

One issue that the voters are raising, according to many of the candidates who have campaigned door-to-door, is Winfield M. Kelly Jr. Many of the slate candidates have reported back to their headquarters at Hampton Mall with word that the only negative comments they hear concern the county executive.

Although Kelly faces nominal opposition in the primary against Vincent Goodsell, John Lee Ball and Eugene Sellner, his own polls show him trailing Republican former congressman Lawrence J. Hogan by a considerable margin. Kelly, armed with a $200,000 campaign chest of his own, has been holding back his money for a radio and newspaper advertising blits in the general election.

Hogan, too, has been relatively quiet during the primary campaign, totally ignoring his primary opponent, Oxon Hill developer Martin Aragona, while preparing for the race against Kelly. Hogan followed the same strategy in his race for governor in 1974 and lived to regret it - he lost the primary to Louise Gore.

While Hogan sits back this time, Aragona, a millionaire, already has gone on television, once and has used a computer-mail technique to identify and send literature to every registered Republican in the county. His campaign has attracted enough attention to convince some weekly newspapers in the county that he will upset Hogan in the primary.