Britain became the first European ally of the United States yesterday to impose bilateral restrictions on its diplomatic and economic relations with Poland and the Soviet Union to demonstrate disapproval of continuing martial law in Warsaw.

The government of Prime Minister Margaret Thatcher announced that it would restrict movements of Soviet and Polish diplomats, refuse to grant new financial credits to Poland, reduce information exchanges with the Soviet Union, introduce a new licensing system for Soviet fishing in British waters and renegotiate a British-Soviet shipping agreement.

A British official in London said in a telephone interview that other NATO allies will take similar steps in the next few days, following weeks of negotiations in Brussels. The allies also have agreed not to reschedule payments this year on Poland's estimated debt of $26 billion to Western banks and governments.

The 10 nations of the European Community are moving to increase the interest on any future export credit granted by Western governments to the Soviets. They also have shifted to private relief organizations money that would have been used for subsidized government-to-government food sales to Poland.

"Not everyone is doing the same thing," the British official cautioned, referring to differences that persist among the allies about how to respond to the Polish crisis. Some countries, such as West Germany, Norway and Denmark, are not expected to take steps as strong as Britain's.

The British actions are largely symbolic and unlikely to affect already contracted British trade with the Soviet Union or Poland. But a British official said they were intended to have the same impact as the U.S. sanctions against Poland and the Soviet Union announced by President Reagan in December.

"They are not really sanctions as such," the British official said, "but a signal to the Polish and Soviet authorities of allied disapproval. We believe this is just as strong a signal as the U.S. measures."

Those measures, taken for the Soviet Union's "heavy and direct responsibility for the repression in Poland," include suspension of flights to the United States by the Soviet national airline, Aeroflot; suspension of licenses to sell an expanded array of gas and oil equipment, which Moscow especially needs for a gas pipeline from Siberia to Western Europe; and the closing of the Soviet Purchasing Commission office in New York, a major conduit of orders for nonagricultural U.S. exports.

Also suspended were licenses for export of "high-technology materials," and negotiations to renew a maritime agreement, meaning stricter controls on Soviet ships calling on U.S. ports. Earlier, Reagan had cut off government-to-government aid to Poland.

The European allies have resisted U.S. pressure to take stronger steps directly affecting their trade with Eastern Europe and the Soviet Union. They contend that it is unreasonable to ask them to risk damage to their economies when the Reagan administration is unwilling to cut off U.S. grain sales to the Soviet Union.

The Soviet and Polish ambassadors to London were informed of the British actions yesterday by Lord Trefgarne, a Foreign Office minister in Thatcher's Conservative government. An announcement also was made in Parliament by Deputy Foreign Secretary Humphrey Atkins, who said the steps would ensure that Britain's "relations with the military regime in Poland reflect the abnormal nature of the present situation."

Polish and Soviet diplomats will be restricted to a 25-mile radius in London, similar to the martial-law restriction on Western diplomats in Warsaw. A British official noted that this would prevent Soviet military attaches from attending military equipment shows outside London.

The anti-Soviet measures, the official said, are intended to reflect "the current context" of relations with the Soviet Union, including both the Polish crisis and Soviet intervention in Afghanistan. They will affect Soviet fishing and shipping in British waters and restrict visits to Britain by Soviet experts seeking information on atomic energy, agriculture, environmental protection and public health.

The Thatcher government also will increase Polish-language British Broadcasting Corp. radio programming beamed to Poland and take steps to counteract Soviet jamming, officials said.