A series of diplomatic clashes between Britain and France, including competition over a $4.5 billion U.S. Army telecommunications contract, have increased the tension in their historically uneasy relationship.

In recent weeks, officials here, including Defense Minister Michael Heseltine, have reemphasized in communications with U.S. officials Britain's contention that it deserves the contract more than France because it is a more loyal U.S. ally.

That point was made in a letter last month from Prime Minister Margaret Thatcher to President Reagan, prompting a French protest and putting U.S. officials in what they said is a difficult position that has caused an indefinite delay in the contract decision.

Both bidders -- Thompson CSF of France and Plessey electronics in Britain, each with U.S. partners -- maintain their product is technically superior. But the French bid is considerably lower and has won initial Army approval.

"If the British get it," said one U.S. official, the issue could "end up in court."

Using the Thatcher letter and other intragovernmental communications, as well as Army tactical evaluations of the two systems, lawyers for GTE, the French partner, could charge that defense procurement regulations were violated through undue political influence, the official said.

"We want the issue to be decided on its technical merits," a senior French official told Washington Post correspondent Michael Dobbs in Paris.

British officials maintain that the battle is simple "competition for a deal," in the words of one. "If it were the other way around, the French would be doing the same thing."

Another official here said "it is well understood that we use whatever leverage we have. One thing Britain has is what's left of the special relationship with the United States."

The British also have some complaints about French behavior. In a little noticed ceremony at the British Foreign Office two weeks ago, the French ambassador was handed an official protest over the sinking in New Zealand of the Greenpeace ship Rainbow Warrior, which was sailing under a British flag.

"We had to respond," an official said. "The minimum we could do was to politely say to France, 'Now that you've admitted it, please remember British interest. We hope you'll give compensation.' "

Barely concealed beneath the diplomatic language, however, was a much deeper indignation here over what had been seen as Paris' suggestion of clandestine British involvement in helping New Zealand catch responsible French intelligence operatives.

In another example offered here, the two governments still differ over an incident during French President Francois Mitterrand's visit here last fall, when British police sniffer dogs discovered explosives in a garden outside the place where he was to dine. They were put there, it turned out, by a French security guard who said it had all been agreed with his British colleagues as a test of procedures. The British said they knew nothing about a jointly agreed test, and suggested it had been an independent French effort to test, and embarrass, them.

For Britain, these are part of a long history of what an official here called "things they do to irritate us." For France, where many still believe, despite denials, that the British were somehow involved in telling New Zealand about French involvement in the Greenpeace sinking, they are proof of what Napoleon called la perfide Angleterre, or perfidious Albion.

"No official will ever admit it, but . . . there is a feeling that the Anglo-Saxons are not unhappy to see what has happened to France" over Greenpeace, said Philippe Moreau Defarges, associate director at the French Institute for International Relations in Paris.

"The French image of Britain is not the simple reverse of the British image of France," Moreau Defarges said. "The British see us as proud and arrogant . . . . The fact that France still thinks it is a great power irritates the English. The French, on the other hand, think the English are hypocrites."

Members together of the European Community, joined in their commitment to western defense, and neighbors for centuries, Britain and France no longer contest territory and kings.

But despite its termination more than five centuries ago, the Hundred Years' War between them is only as distant as the nearest history book for schoolchildren on both sides of the English Channel, or La Manche, as it is known on its southern shore.

More recently, their rivalry has taken place through decades of bruising battles over the Common Market, beginning with British refusal to join when it was formed in the 1950s, through French president Charles de Gaulle's subsequent veto of Britain's application in the 1960s, to the angry battle over the community budget last year.

Both sides say that tempers have cooled considerably with the replacement of former French foreign minister Claude Cheysson by Roland Dumas.

"Mr. Cheysson," said a British official of the Frenchman, who reportedly attributed French difficulties in dealing with Thatcher to gender, "had a tendency to speak off the cuff."

The competition for the U.S. contract is a reflection of British-French rivalry for defense sales around the world. Britain, with 6 percent of the world market, and France with 8 percent, are both eager to expand their share.

When India was shopping for a new jet fighter aircraft, France's Mirage 2000 beat out a competing bid by the British Tornado. Last spring, France reportedly was on the verge of selling the Mirage to Saudi Arabia, only to have the deal fall apart over Saudi insistence that part of the price be paid in oil. Three weeks ago, Britain accepted similar terms and sold the Saudis $5 billion worth of aircraft.

Competition also has reared its head in West European defense collaboration projects. Agreement on a five-nation effort to build a new generation European jet fighter was held up for months this year as France and Britain each argued that its design was superior. The British design eventually won the approval of other partners West Germany, Italy and Spain. France rolled up its blueprints and went home, refusing to participate in the fighter deal.

Amid the arguments and the competition, however, British officials point to some success stories. The EC budget battle eventually was resolved last year to the satisfaction of both sides. There has been collaboration on projects like the Airbus civilian aircraft and maritime satellites, and a joint contract proposal is pending for a new nuclear power facility in China.

Early next year, the two governments will collaborate on selecting one of competing joint private Anglo-French proposals to build a tunnel under the channel.