The search for an alternative to the Reagan administration's sanctions against the Soviet natural gas pipeline continued yesterday with a meeting between senior State Department officials and ambassadors from four major European countries. Another meeting is scheduled for this morning.

Today's session will be the fifth in two weeks on the issue. It follows expressions of optimism by Italian Prime Minister Giovanni Spadolini -- after a meeting with President Reagan on Wednesday -- that a solution could be found "very soon."

Diplomats involved in the talks have been more circumspect.

West German Ambassador Peter Hermes said on leaving the State Department yesterday afternoon that officials were "very close" to an agreement. But the chief U.S. negotiator, Undersecretary of State Lawrence S. Eagleburger, refused any characterization when asked about the talks at a diplomatic reception last night.

Eagleburger said he did not expect a decision at today's meeting, but he did not rule out the possibility. He would not put a deadline on the current round of negotiations, but added: "I can't go on with this forever."

Yesterday's talks originally were supposed to have included ambassadors from the major European countries, Japan and Canada, plus the Danish ambassador as a representative of the European Community. Denmark is current chairman of the community.

Eagleburger said last night, however, that the envoys from West Germany, Italy, Britain and France -- the four countries with companies under sanctions -- had requested a meeting with him.

The four ambassadors reportedly met on Wednesday after Secretary of State George P. Shultz had outlined to Spadolini and Italian Foreign Minister Emilio Colombo the latest administration thinking on a proposed agreement.

The document under discussion is believed to contain a general statement of the allies' determined desire for accord on the strategic role of East-West trade and then to define specific subjects such as credits, limits on energy dependence, and strengthened limitations on trade in high-technology items having military application.

What to include in the definition of credits is said to be the main sticking point in the discussions, assuming that all the countries involved are determined to reach an accord. The United States is said to want to spell it out in detail, while the Europeans are pressing for a more limited statement that simply would commit the countries to "harmonize" their policies on credits for trade with Moscow.