Export-Hungry Japan received a stern warning from British Trade Secretary Edmund Dell today to change its trading policies or risk destriction of the world's free trade structure.

Noting the British Governments "deep concern" over the world economy, Dell said: "We see gave danger that . . . the open trading system will be eroded, at first perhaps only at the margins, but then ever more rapidly and decisively.

"I hope that Japan would accept that if, in the present world situation, any action exploits its competitive strength without regard to the consequences (in other countries), its successes will prove to be counter-productive," the Trade Secretary said.

In a remarkably strong speech, Dell attacked Japan and West Germany by name for accumulating trade surpluses and thereby contributing to unemployment and economic difficulties in other countries.

"If by competitive successes the employment situation of trading partners is seriously worsened," he warned," that will increasingly endanger the whole system."

British ran a $700 million trading deficit with Japan, in 1976 and Dell complained that British exports were handicapped by discriminatory charges, high tariffs, overpricing and general Japanese resistance to British imports.

The Trade Secretary's stinging admonition was administered less than 24 hours after he arrived in Tokyo on a five-day consultation mission and was repeated in private sessions with Premier Taakoe Fukuda and Minister of International Trade and industry Tatsuo Tanaka according to Japanese officials.

Japan has come under international cirticism for amassing an $11 billion trade surplus last year when most industrially advanced nations were still suffering from the recession caused by the oil crisis and incurring deficits. Prior to today, the complaints were genteel and discretely worded. Certainly no foreign government official has approached the blunt message and somewhat menacing tone of Dell's address at a Foreign Correspondents Club of Japan luncheon.

The battle for export markets was increasing in bitternerss Dell said, as nations struggled to maintain employment and cut down on balance of payments deficits they were eager to export, reluctant to import. Preservation of open trade would grow more difficult unless all major industrial countries co-operated in adjusting to the new wealth of the oil-producing nations.