Italian Prime Minister Giovanni Spadolini said yesterday after talks with President Reagan that the United States has proposed a new Western policy on strategic trade with the Soviet Union and that a "solution" to the divisive Siberian gas pipeline question "is very near."

The proposals, which reportedly were discussed informally by some European ambassadors yesterday, are to be outlined at the State Department today in the fourth meeting of high-ranking U.S., European, Canadian and Japanese diplomats on the issue in a week and a half.

A State Department official closely involved in the talks said yesterday it is now "60-40 that an agreement can be reached."

The more optimistic tone of yesterday's comments ran sharply counter to suggestions from both sides of the Atlantic earlier in the week that there seemed to be a lack of political will in Washington and in the European capitals to reach an agreement.

"The Western world must find and define a common approach based on a greater strictness of an economic nature in its relations with the Eastern world," Spadolini said after he met with Reagan for an hour and a half yesterday.

He said the approach must be "based on and inspired by" four points, going further than any official has yet done to outline in public the proposed agreement that has been under discussion for a month:

"First, no undue gift to the Soviet Union as far as credits are concerned. Second, greater strictness in the transfer of technologies to the Soviet Union. Third, implementation of a security net within the western system so as to reduce the dependence on the Soviet Union concerning raw materials and energy products. Fourth, the contracts that already have been signed by European countries concerning the pipeline must be honored so as not to prejudge the credibility as far as the trade of the Western world is concerned."

A senior U.S. official said yesterday that the first three points are "virtually drawn from the papers" that the Europeans and the United States have been exchanging.

The official said of the fourth point, a clear reference to lifting of the pipeline sanctions, that there is no explicit agreement and indicated that some European countries might not favor having a clear linkage in the document.

It is likely to happen, the official said, but "not immediately; not directly."

The U.S. position reportedly was first outlined to the Italians at a morning meeting with Secretary of State George P. Shultz. Italian Foreign Minister Emilio Colombo, who is accompanying Spadolini, then reportedly consulted by telephone with French Foreign Minister Claude Cheysson and West German Foreign Minister Hans-Dietrich Genscher before the White House talks.

Ambassadors from the four European countries that have companies under U.S. sanctions -- Italy, West Germany, France and Britain -- also are reported to have met yesterday. The sanctions bar companies that ship goods for the Soviet gas pipeline from receiving any U.S.-made equipment related to gas or oil; they were imposed in response to the declaration of martial law in Poland.

Reagan was more cautious in his remarks at the White House departure ceremony, saying only that he and Spadolini "agree that the United States, Italy and the other allies must pursue discussions aimed at establishing a broad transatlantic consensus."

U.S. officials long have pointed to an agreement on credits, transfer of high technology goods and limits on energy purchases as an acceptable alternative to the sanctions policy.

European diplomats say that the agreement being negotiated contains a commitment to study these points, with an ultimate agreed policy being the end goal, and in the meantime a moratorium on purchases of energy from Moscow and sales of high technology goods to the Soviets.

Left to be negotiated, however, are the definitions of terms that will be the subject of the studies, and diplomats on both sides of the Atlantic say there still are some key differences, particularly over how to define the credits issue.

"Indeed there are some problems, especially when we talk of harmonization of credit policies," a senior European diplomat said yesterday. "This is especially true given the different systems of credit in the different countries."

Diplomatic sources hinted yesterday, however, that it was in this area that the latest U.S. position appears to be showing a "greater understanding" of the needs of the Europeans.

Spadolini is in the United States for an official visit that also is to carry him to New York and the West Coast.

While the focus of yesterday's talks clearly was on the troublesome trade issue, Reagan and Spadolini also said they covered a number of other issues on which the two countries have been cooperating closely.

Italy has emerged as a pillar of U.S. policy interests in Europe and elsewhere over the past couple of years, as reflected particularly in its participation in the Sinai and Lebanon multinational forces and in its decision to take the lead in installing a new generation of medium-range nuclear missiles.

Officials on both sides of the Atlantic have expressed fear that differences over the pipeline sanctions could spill over to affect other issues, especially the cooperative spirit on the missiles, which are to be installed beginning in 1983 and which are politically sensitive to the host governments.

The pipeline issue "goes into other problems of 1983; not directly, but there is a clear spillover," a top-ranking U.S. official said yesterday.

Spadolini also announced yesterday at the White House that Italy has decided to purchase 30 McDonnell Douglas DC9 aircraft, a deal that U.S. officials said is worth more than $800 million.

Later, Spadolini seemed to qualify his announcement. At a press conference at the Italian Embassy, he said that the purchase would come "once the trade situation between the two countries is normalized," an apparent reference to the pipeline sanctions.

Italian officials said the prime minister did not want to draw a formal connection between the two issues and merely was referring to the likelihood of the sanctions issue being resolved in the time it takes to work out details of the plane purchase. An administration official said it was likely that Spadolini's statement was made in the expectation "that things are going to return to normal. He has the feeling we are going to work things out, and so do we."

Spadolini said in his White House remarks that he would discuss his White House talks with French President Francois Mitterrand when he visits Paris on Nov. 12. In his press conference later, however, he said that he hopes a general agreement will have been reached by that date and only technicalities will be left for discussion.