Gains in relations with western countries and a strong endorsement from the Soviet Union have strengthened the leadership of Gen. Wojciech Jaruzelski before an important communist party congress but have failed to improve prospects for Poland's crippled economy, government officials and diplomats here say.

An official visit by Foreign Minister Marian Orzechowski to West Germany last week confirmed Jaruzelski's slow progress in his drive to normalize ties with western governments after a four-year freeze. Bonn recently extended its first trade credit to Poland since 1981, and Chancellor Helmut Kohl called for a general improvement in relations between the two countries.

The visit followed a month in which Jaruzelski had his first high-level contact with a representative of the Reagan administration and was singled out for praise among Eastern European leaders by Soviet Foreign Minister Eduard Shevardnadze.

At the same time, officials of the Roman Catholic Church signaled that Pope John Paul II would be willing to meet with Jaruzelski for the first time at the Vatican.

The developments have been hailed by Jaruzelski's advisers as a major boost that will ensure his ability to consolidate his leadership and push through his government's policy agenda at the party congress in June. In the past, Jaruzelski's failures in diplomatic initiatives have helped fuel discontent with his rule among the party's conservative sectors, these advisers said.

However, both government officials and diplomats say that the foreign policy successes seem unlikely to produce the economic assistance Poland needs to rebuild its economy. Moreover, further improvements in western ties appear conditioned on domestic political and economic initiatives that Jaruzelski has been unwilling to take.

"The results of the big campaign are not all that tangible," a western diplomat said. "If you add it all up, it's a slight plus. But the Poles are very bankrupt, and what they need is somebody to come along with a lot of money and good will to help them. That isn't happening."

The continuing barriers in foreign relations were apparent last week as government officials announced that they had postponed a planned visit by Orzechowski to Britain this month. Diplomats said the trip was called off because Orzechowski had been unable to arrange a meeting with Prime Minister Margaret Thatcher, who has conditioned the contact on moves by Jaruzelski toward political liberalization.

The setback followed a similar failure by Jaruzelski in February to arrange an official visit to Italy and a meeting with Prime Minister Bettino Craxi, who has strongly objected to Poland's continued detention of leaders of the banned Solidarity trade union. Diplomats said the impasse with Rome probably would make it impossible for Jaruzelski to arrange a meeting with the Polish-born pope at the Vatican before the party congress.

A potential warming in U.S.-Polish relations was signaled by the visit here last month of former U.S. ambassador Walter Stoessel, the highest-ranking American emissary to meet with Jaruzelski since President Reagan came to office.

However, sources here said the meeting has yet to produce concrete results. U.S. officials had hoped that the contact with Stoessel, a retired deputy secretary of state who nominally met with Jaruzelski in a private capacity, would spur Warsaw to take a reciprocal initiative to improve ties.

Nevertheless, "nothing has come out of the meeting," a diplomat here said, adding that the two sides "had nothing new to say" in the talks. "The results will depend on decisions made in both capitals," the diplomat added, "but there have been no results to date."

The stakes in Jaruzelski's foreign policy were illustrated last week as government officials struggled to reschedule payments due to western banks on Poland's $29 billion foreign debt. Unable even to pay off accumulated interest on its loans, the government has been forced for the fourth year to plan cuts in imports and investments while adding unpaid interest to an already unmanageable debt burden.

Economic officials have stressed that Poland will be unable to pay its debt or modernize and stimulate its stagnating industry without new credits and greater concessions on outstanding loans. But banks have consistently refused to extend fresh funds, and virtually the only new money Poland has received has been the $45 million in trade credits granted last month by West Germany.

Although significant in political terms, the German credit was minor compared to the $800 million Poland hoped to receive from western governments after a major rescheduling agreement last year. Efforts by Orzechowski to win expanded assistance from Bonn in last week's visit were turned down, diplomatic sources said.

At the same time, the growing warmth in Jaruzelski's relations with Soviet leader Mikhail Gorbachev does not appear to have resulted in new economic assistance by Moscow. Poland remains pressed to reduce its trade deficit and debt with the Soviet Union, and a recent effort by Prime Minister Zbigniew Messner to win more favorable terms for Soviet energy supplies to Poland was rebuffed, according to sources.

"Gorbachev has been a much better partner for us," said a communist party official close to Jaruzelski. "But it is not an ideal situation; in the economic field you can never get all that you want."

The increasing deterioration of the economy and industrial base brought on by the payment and credit difficulties has caused even some opposition leaders to hope Jaruzelski can soon break the impasse in western assistance.

"The isolation of Poland could have a disastrous effect in the long term without serving any real political purpose," said an adviser to Solidarity who met with Stoessel during his visit here. "I'm afraid that Poland could be permanently excluded from the economic development in Europe."

However, western officials say that Jaruzelski's diplomatic initiatives inevitably have been stalled because his domestic policies are likewise stalled. Even while aggressively seeking western contacts in the past six months, the government has continued to hold hundreds of political prisoners, has tightened control over intellectual life and has allowed a flagging program of economic reforms to stagnate.

In February, Jaruzelski appeared close to taking major steps to satisfy western and internal concerns. The cases of three imprisoned Solidarity leaders were brought before the Supreme Court for review and high government officials told Catholic bishops that approval for a church-sponsored fund for private agriculture strongly supported by western governments would soon be granted.

The concessions never materialized, however, and government officials say Jaruzelski now is not prepared to implement new measures before the party congress.

"We must have more time before the next liberal steps in Poland," a party source said. "Now we must address not the audience of the West, but that of the party, and in the party there are too many votes that say the leadership has already been too liberal."