When Marty Horneber's independent service station in Northern Virginia was gutted by fire last Janurary, his ongoing skirmish with Citgo, his supplier, soon turned into a one-man war.

The 51-year-old dealer was already being pressured to shut down his Annandale station so that the giant oil company could open one of its own, and the fire was an accident that Horneber says gave Citgo an excuse to cancel his franchise lease.

The staton was insured, but Citgo refused to authorize its rebuilding. And, when the determined dealer moved a trailer office onto the site and continued pumping gasoline, the company seized his Citgo logo, took back company credit card machines and raised the cost of the gasoline it sold him by 4 1/2 cents a gallon.

"They just came in and unbranded the station," said Horneber, whose battle with Citgo has turned into something of a cause celebre with independent dealers in the area.

In the meantime, Horneber says his business' gross income has dropped to about $800 a day from its former range of $1,400 to $2,000 daily. Out of that he must meet Citgo's nearly doubled rent of $3,300. He has no electricity, so his station is shut down at night. He operates his garage lift by hooking up an extension cord from his trailer. And he has had to cope with questions from local building inspectors and health officials about the safety of his gutted building.

Such strong-arm tactics, the independent dealers say, were why they turned to the state legislature two years ago to stop the big oil companies from opening any new company-owned statons with 1 1/2 miles of any station operated by an independent dealer. The law was intended to protect the independent dealers and was similar to an even tougher protective measure adopted by Maryland legislators.

At first dealers like Horneber breathed a sigh of relief, confident that the oil companies had been discouraged from trying to take over their stations. But then, some dealers encountered new problems.

Just five days before the law went into effect, a Citgo dealer vacated his station in Fairfax County and moved to a less lucrative site in Manasses. The reason, according to Ron Harrell, vice president of the 1,200-member Virginia Gasoline Retailers Association:

"He was paying very high rent in relation to what he was pumping, and Citgo wanted his staiton so much they offered him a cheaper site in Manassas. But they told him he had to take the deal right then -- before the law took effect -- or lose it."

Then, last Jan. 31, one of Horneber's attendants was repairing a gasoline tank and dropped it in the station's garage while trying to drain it. The sparks ignited the gasoline fumes, and the fire started immediately. Horneber's five-year lease was due to expire in September 1981, but Citgo cited a clause in the contract that allowed the agreement to be voided in cases of fire.

In August, company representatives came calling. They left with all traces of Horneber's Citgo identificaton. The firm put the dealer on a month-to-month lease and announced that they wanted him to vacate the site so they could open it as their own.

"It's the Citgo-type operations that have caused the problems in the industry," said Harrell. "The gasoline volumes in Northern Virginia are quite appetizing to the oil companies, and for some of them the policy has been to do everything they can to move the dealer out."

"Citgo has wanted this station for years, and it's obvious they're trying to starve the guy out," said State Sen. Richard L. Saslaw, the Fairfax Democrat who sponsored the protective legislation for the dealers. "The dealers have told me that Citgo is one of the worst companies to work with -- they're almost ruthless in their method of dealing with their own people."

Even before the fire at Horneber's station, the dealer said, Citgo lowered gasoline prices at two Citgo-operated statons "at my front and back doors" in what he said was an effort to increase competitive pressure on him.

Saslaw said the oil company would be violating Virginia law if it tries to open its own station on Horneber's site, on a busy corner just below the Burke Village Shopping Center.

The Northern Virginia legislator said he has driven between Horneber's staiton and two nearby independent dealer operations and has found them both to be within the 1 1/2-mile restriction. If Citgo tries to operate out of the station, he said, the Virginia Gasoline Retailers group will take them to court.

Citgo spokesmen in Tulsa dispute Saslaw's interpretation of the law. They say they lost one station in the area because of road condemnation proceedings and thus have a right to take over the Burke site. They have offered to trade Horneber two stations in Maryland -- which they are being forced to give up because of the Maryland law -- for his one station in Northern Virginia. Horneber is not keen to relocate, and say that the two Maryland stations are less lucrative and would require him to commute between his home in Annandale and stations in Wheaton and Oxon Hill.

"We didn't come up with some special provisions to get him out," retorts John Singleton, a Citgo public relations officer. "It was a business decision -- if it's desirable and profitable to have a company-operated station, then we will strictly observe any contract provisions that would give us the option of opening such a station."