Key Carter administration officials have warned Japanese Foreign Minister Sonoda that two touchy trade issues must be solved before Japanese Prime Minister Masayoshi Ohira visits President Carter here in early May.

In a series of meetings in the past two days with Treasury Secretary W. Michael Blumenthal. Special Trade Representative Robert S. Strauss, and Secretary of Commerce Juanita Kreps, the Japanese foreign Minister was asked to convey a sense of urgency to his government in Tokyo.

Sonoda responded by suggesting that Strauss visit Tokyo in the next few weeks to convey to his government the importance to which the U.S. government attached new trade concessions.

Officials here said privately that the Japanese government apparently would utilize such a Strauss mission to help put the pressure on various parts of the Japanese bureaucracy "that need to be convinced."

Stauss said in a telephone interview that he would make no decision on such a trip unless there were "hard commitments" in advance by the Japanese.

Specifically, the American group told Sonoda it wanted assurances that would open Japanese procurement for the Nippon Telephone & Telegraph System to competitive bidding for sophisticated equipment, and an agreement that would avoid delays in putting into effect tariff cuts to which Japan has already agreed as part of the multilateral trade negotiations (MTN) in Geneva.

Coincidentally, Japanese Finance Ministry official Michiya Matsukawa said in a separate interview that the recent decline in the Japanese yen-which he said had gone too far-"is not a sign of a new currency turmoil." Matsukawa also rejected the idea that the yen had depreciated enough recently to touch off a new wave of imports into this country. The yen has declined from about 185 to the dollar last October to about 215.

Tension between the U.S. and Japan on trade issues stems from a bilateral Japanese surplus with this country that ran about $13 billion last year.

There are some signs that the surplus is beginning to shrink, reflecting last year's appreciation of the yen. Matsukawa cited new figures which show that on a volume basis, Japanese imports (worldwide) had increased 14.9 percent in February, compared to the same month in 1978, while export volume had diminished by 14.2 percent.

But American officials fear that over the medium and long range, there will be little permanent improvement unless Japan takes decisive steps to open up its import market to manufactured goods.

On a recent visit here, special ambassador Nobuhiko Ushiba proposed to open a large volume of orders for NT&T to competitive bids, but Strauss rejected the offer because it did not include sophisticated equipment. He accused Japan of following a "Buy Japan" policy.

The issue of timing tariff cuts is more complicated. Japan is the past several years had made many unilateral tariff cuts below the stipulated (bound) rates of the General Agreement on Tariffs and Trade (GATT). New reductions are contemplated by the new MTN agreement.

The question at issue is whether Japan should make the MTN cuts from the bound rates, or from the lower actual rates already in effect, Japan argues that, legally, the cuts should be made from the bound rates. The U.S. position is that the reductions should be made from the actual rates. Otherwise, U.S. officials say, further reductions in Japanese tariffs will be delayed two or three years.

The Japanese respond that to follow the American position would penalize them for voluntarily having made reductions ahead of time. But officials at yesterday's and Monday's meetings say that Sonoda appeared to recognize, nonetheless, that Japan may have to make further concessions.