Soviets find it hard to keep supplying Poland

Polish martial law chief Wojciech Jaruzelski has won a pledge of continued Soviet economic aid, while assuring the Kremlin he plans a strictly controlled program of reform-from-above at home.

At least that is the impression of a joint communique capping General Jaruzelski's two-day visit here, a visit that found the Soviet Union and Romania facing economic strains of their own.

For Moscow, in particular, these strains could well worsen if the Polish economy does not start working markedly better. One key factor, Western diplomats suggested, would be whether the general's apparent vision of ''reform from above'' proves workable.

The communique, printed March 3 in Soviet newspapers, quoted Jaruzelski as saying his nation would ''continue the line of the ninth (Polish Communist Party) congress,'' a session held last July that committed Poland to the process of ''renewal'' won by the now-disbanded Solidarity union movement.

''It was stressed by the Polish side that any attempts to resume actions aimed at causing economic disarray, at resumption of anarchy, disturbances, at changing the social and political system, will be cut short most resolutely in the future, also,'' said the communique.

In a banquet speech on the first day of his visit, General Jaruzelski spoke of continuing the ''general line of the ninth congress.'' The vow to crack down hard on any renewed unrest came only in the final communique.

That led some Western analysts to assume the two sides had agreed on the need for some sort of continued reform - a search for long-term political entente to facilitate genuine economic recovery - but that Moscow wanted this done in the strictest way practicable.

Meanwhile, Jaruzelski's visit provided a fresh reminder of the economic costs for Moscow of the Polish crisis. The Polish leader said his country's economy remained in a ''very grave'' state. It needed a ''strong additional impulse,'' and ''Soviet assistance is that impulse.''

The final communique, while committing Poland to ''efforts'' to revive flagging exports to the USSR, pledged Moscow to ''continue to render support and assistance.'' No details were given. A senior official here said privately that further Soviet aid would include installments to ''fill gaps'' no longer plugged by the West. He did not elaborate.

The pledge of aid came at a time of considerable economic woe for the Soviet Union itself. Coping with its third poor grain harvest in a row, faced with pervasive shortages of meat and some dairy products, the Soviets must shell out coveted hard-currency assets for grain imports.

Many Western sources here assume the Soviets have helped Poland come up with some recent, piecemeal payments on its enormous debt bill, although there has been no convincing confirmation of this. There have been signs of something of a Soviet hard-currency crunch:

* In a move one economic publication (Britain's Economist magazine) says has no postwar precedent, the Soviets recently asked various West German and Japanese companies for extra time to pay debts already due.

* Western sources say Moscow has been selling uncommonly large amounts of oil , diamonds, and gold in a bid for quick hard-currency earnings. (Last October, in a rare official statement on gold policy, the head of the Soviet state bank said that despite Moscow's high priority on building up gold reserves, there was a readiness to ''sell gold to overcome disproportions'' in trade with the West.)

* Western business sources here say transactions involving hard currency have recently become subject to a tightened process of review by senior Soviet officials.

* Britain's Reuter news agency has reported that, since the start of the year , jittery Western banks have begun charging Moscow a premium - one-eighth of 1 percent - on loans on the interbank market.