By tonight, the fireworks business should be booming.

In a matter of hours, as darkness marches across the United States, more than $100 million worth of imported and domestically made fireworks will go up in sparkle and smoke.

Ironically, most of the red, white and blue rockets whooshing across the sky and other fireworks used to celebrate the great American holiday will be imports from what used to be known as Communist China.

"The biggest trend is the continued increase in merchandise from the People's Republic of China," said John Conkling, executive director of the American Pyrotechnics Association. "They've just dominated the import market," he said.

Roughly 60 percent to 70 percent of the fireworks now sold in the United States are imported from mainland China, which sent some 27.2 billion firecrackers, sparklers, fountains and other items worth approximately $23 million to the U.S. in 1980.

"The advent of trade with China is probably the single biggest thing that has happened in the industry," said Charles Shivery, president of the Elkton Sparkler Co. in northest, Md. The China trade quickly took business away from other eastern countries including Taiwan that had supplied the bulk of fireworks imported to the U.S. before former President Richard M. Nixon opened trade with China.

American factories have generally left the small and labor intensive items to foreign manufacturers whose low labor costs allow them to produce more cheaply.

In spite of foreign competition, American manufacturers continue to hold their own in the battle for the transifxed stares of their countrymen. Elkton, Md., judging from the labels on locally sold fireworks, appears to be a center of fireworks manufacturing.

The Elkton Sparkler Co. is the largest sparkler manufacturer in the U.S. and one of the largest in the world. Shivery's father worked in another fireworks manufacturing plant that went into the munitions business during World War II and later closed. In 1945, the senior Shivery opened his own firm, which his son now heads.

All year long, the factory produces sparklers from the raw material to the finished product -- straightening and cutting wire, dipping the end of the wire in a solution of barium nitrate, aluminum powder and crushed iron.

The busy season is April, May and June when the staff reached 60 to 70 workers producing sparklers that are distributed through chain stores such as 7-Eleven. "We're beyond the busy time now," said Shivery on July 2. "We're just cleaning up the odds and ends." Shivery celebrates his Fourth of July at poolside, sans fireworks. "I see enough of them during the year."

Fireworks have enjoyed something of a resurgence in the past few years, according to Conkling. In 1976 the Consumer Product Safety Commission put into effect regulations governing the types of fireworks that may be legally sold to the public. Some areas that previously had total bans on the use of fireworks have relaxed the ban since then, allowing limited items.

The trend appears to be more legal fireworks but of the sort that deliver less bang for the buck. Several states ban aerial fireworks and firecrackers. lFederal standards limit firecrackers to 50 milligrams of powder.

Eightenn states allow the items allowed under federal standards; 35 permit some type of fireworks. A total ban is still in effect in 15 states, mainly those in the northeast. Maryland, Virginia and D.C. all allow some types of fireworks, Conkling said.

"Backyard fireworks have been increasing in volume, but public displays certainly haven't decreased in number," said Conkling. "There was a big jump in 1976, and a number of towns have kept having them," he said.

Although chain stores carry limited types of fireworks, most are sold from temporary stands erected for holiday sales. Although some stands are run as fundraising projects for civic groups, most of the stands in the Washington area are run in individuals.

"I started it as a summer job for the kids when they were young," said Donald Stivers, a Department of Defense employee whose family has operated a stand at Connecticut Avenue and Morrison Street NW for eight years. Stivers' daughter Donna runs the stand now with her younger brother Michael's help, and her sister Rosie runs a stand on Wisconsin Avenue.

The Stivers buy from a wholesaler, Washington Fireworks, pick up their occupancy, fire and construction permits and vendors licenses and open their stands approximately two weeks before the holiday.

"This year there are more stands in the Washington area than ever have been," said Stivers. "It gets around by word of mouth that it's a way to make a good profit in a short time," he said.

The mark-up on the products is about 50 percent. In a good year, profits can exceed 30 percent return on investment. "But it's a gamble," he said, peering from the back of the rental truck he was unloading as the clouds threatened.

With heavy rain the selling season might end not with a bang, buy a whimper.