The Carter administration will ask Congress shortly to approve a most-favored-nation trade agreement with China even though the move could disturb the U.S. policy of dealing with the two communist superpowers China and the Soviet Union -- in an even-handed manner.

State Department sources said yesterday the pact with China, which was initialed by Commerce Secretary Juanita Kreps in May, will be signed within the next few days and probably will be submitted to congress later this month.

However, the sources added the administration does not plan at this time to seek congressinal approval of a similar agreement with the Soviet Union. An accord granting most-favored-nation status to the Soviets was signed in 1972, but it has never been submitted to Congress.

Approval of the agreement granting tariff benefits to the Soviet Union has been blocked by a congressional prohibition, the Jackson-Vanik Amendment, denying such status to countries that fail to allow liberal emigration of their citizens.

In the Soviet case, the problem primarily has involved restrictions on the outflow of Soviet Jews. The Soviets have relaxed these restrictions considerably during recent months, and, for a time, there were hopes within the administration that Congress could be induced to waive the Jackson-Vanik bar to an agreement with Moscow.

However, at last month's Vienna summit, President Carter failed to obtain from Soviet President Leonid L. Brezhnev an explict statement on continued Jewish emigration that would have satisfied the Jackson-Vanik requirements.

By contrast, China has met the requirements for a congressional waiver by giving assurances it will not interfere with emigration of its citizens. Since the opening of U.S. Chinese diplomatic relations in January, pressure has been building steadily on both sides for a pact allowing greater exploitation of trade by the two countries.

That posed a dilemma for the administration, which had been chary of doing anything that might raise new Soviet suspicious about Washington playing the so-called "China card" giving special benefits to Peking in an effort to set it against Moscow.

However, the sources said, after the Vienna summit, the administration, recognizing that it would not be possible to move ahead on trade pacts with both countries simultaneously, decided to act on the Chinese agreement alone.

In making the decision, the sources added, the administration was influenced heavily by warnings from congressional leaders that quick action is required if the accord is to be approved this year.

The sources said the Soviets are aware of the U.S. decision and added that the administration is hopeful the move will have minimal effect on U.S.Soviet relations.

The sources also said that if the rate of Jewish emigration -- currently at a level that could mean 50,000 emigrants by the end of the year -- continues, he chances may be good that the administration will sound out Congress again within a few months on removing the restrictions against the Soviet Union.

Most-favored-nation status is enjoyed by the vast majority of countries with which the United States trades. The status means lower tariff suties than are applied to imports from countries that don't have this status, thereby putting those nations without it at a competitive disadvantage in selling goods to the United States.

That has been the situation of the Soviet Union as the result of the amendment sponsored by Sen. Henry M. Jackson [D-Wash.] and Rep. Charles A. Vanik [D-Ohio]. Their amendment, coupled with a $300 million limit on Export-Import Bank credits to the Soviet Union, led Moscow in 1975 to repudiate the 1972 trade agreement.

The agreement with China does not include access to credits from the Export-Import Bank, which provides long-term, low-interest financing for foreign purchases of U.S. goods.

The sources said an agreement on Export-Import Bank credits had to be held up pending resolution of debts owed the bank by the Nationalist government, which preceded the communist regime on the Chinese mainland. The sources said that matter is being untangled and the expectation is that China will be in a position to receive Export-Import Bank credits within the next few months.