MANAGUA, Nicaragua (AP) _ Fresh from giving the new U.S.-backed government a political drubbing, the Sandinistas have taken charge of celebrating the 11th anniversary of the Nicaraguan revolution.

July 19 is a national holiday, but the party will be pure Sandinista.

Banners, red-and-black party flags and Sandinista posters were being trucked over to a downtown plaza Wednesday.

Workers were nailing together the platform where dancers and musicians will entertain Thursday and former President Daniel Ortega will speak.

Ortega, intent on capitalizing on his party's most recent political victory, has been behaving as though he were still in office, presiding at public rallies, inaugurating water pipes and roads, and speaking at induction ceremonies for new Sandinista militants.

Barricada, the party newspaper, has been feasting on the party's apparent resurgence. It has been running a banner at the top of its front page proclaiming: ''The Revolution Continues ... Not one step back 3/8''

Stronger and more defiant than at any time since losing the Feb. 25 elections, the Sandinistas have been exhibiting their superb knack for organization.

Neighborhood parties complete with clowns, musical groups and speeches have preceded Thursday's big bash by the Sandinistas, the only organized public event marking the 1979 fall of the Somoza family dictatorship.

''It's not their holiday,'' said Zoila Lara, an anti-Sandinista domestic worker. ''If everybody hadn't helped them (in 1979), they wouldn't have done anything.''

The new government has limited itself to declaring July 19 a national holiday commemorating ''the Nicaraguan people's triumph over the Somoza dictatorship, an undeniable fact of the unity of all social, political and economic sectors of Nicaragua.''

The Sandinistas quickly consolidated their power after the revolution ousted dictator Anastasio Somoza and held onto it until voters rejected them for a conservative, pro-U.S. coalition.

The Sandinistas have waged a campaign of labor unrest since the April 25 inauguration of President Violeta Barrios de Chamorro that has forced her to make broad concessions.

The last strike stopped just shy of civil war between Sandinista sympathizers and government supporters. It ended when the government agreed to negotiate even before Sandinista-manned barricades reminiscent of the 1979 revolution had come down in Managua, the capital.

The 10-day Sandinista-led strike was settled with an agreement that grants hefty wage hikes to government employees, pledges no mass firings of public sector workers and puts some key elements of the new adminstration's plan to return Nicaragua to a free-market economy on hold.

The Sandinistas hailed the settlement as a victory. Mrs. Chamorro said it had prevented bloodshed and unrest. The business community and some leaders of the governing coalition said it had set back the new administration's economic recovery program.

A week after the strike's end, work crews were still replacing paving stones uprooted for the barricades and traffic was jammed at key intersections.

The Sandinista celebration will be held at what the leftist party still calls the Plaza of the Revolution despite the fact that Mrs. Chamorro's government has changed its name to the pre-revolutionary Plaza of the Republic.