The Soviet Union is beginning to signal snags and economic sacrifices in its bid to counter President Reagan's gas-pipeline sanctions.
Most diplomats and foreign business sources here still feel that Moscow's centrally run economy will ensure completion of some kind of new Siberia-Western Europe gas link by the current target date of January 1984.
Besides, these analysts say, the Soviets can almost certainly meet initial gas-delivery requirements by making use of excess capacity in a smaller export pipeline built in the 1960s.
A recent edition of the Soviet government newspaper Izvestia added that a planned Czechoslovakian pipeline to link the new Siberian export conduit with the West European gas grid would operate at ''full capacity'' only from 1988, but that this would not affect European deliveries contracted for earlier.
And on the political front, the men in the Kremlin can hardly be mourning the rancor within the Western alliance caused by Mr. Reagan's June 17 expansion of US sanctions against the gas-line project.
But the official Soviet news media have recently given a number of indications that building the new pipeline around the US trade restrictions will be trickier than initially suggested.
The first problem - and the one, in the view of foreign analysts, least complicated to counter - is the overall pace of work on the line. Although most Soviet accounts have included routine statements that work is going well, and that the pipe link will be done on or ahead of schedule, the Communist Party newspaper Pravda struck a discordant note in an article Aug. 18.
It said government officials had concluded that workers clearing the line's roughly 2,700-mile route - through some 450 miles of swampland, 90 miles of permafrost, over 561 rivers or streams, and across both the Ural and Carpathian mountains - would have to step up their pace by ''two or two-and-one-half times'' to stay on schedule. So, the newspaper said, would crews doing the rest of the pipeline project: constructing living quarters, laying pipe, and setting up 41 compressor stations.
The Pravda article seemed to imply that general snags in Soviet pipeline construction detailed in earlier accounts published here were hampering the Siberia-West Europe project as well. These include shortcomings in planning and management, in equipment, and in transportation.
The antidote, foreign diplomats assume, is to ensure top priority within the Soviet economy for the current pipeline project - something the Soviet authorities are clearly moving to do, in hopes of making the pipeline a dramatic symbol of Soviet immunity to American ''diktat.''
(A CIA analysis prepared in August concludes that the Soviets will be able to meet their gas delivery commitments to Western Europe ''through the 1980s,'' despite the Reagan administration's sanctions.)
But if one strength of the Soviet economy is the prerogative to set such priorities centrally, one weakness appears in handling various ''priority'' projects at once. The Siberian pipeline is competing with other major works already encountering problems of infrastructure and equipment, for instance, the BAM trans-Siberian railway. That rail line is intended as a centerpiece for a new spurt in Siberian resource development later in this decade.
A second challenge for the Soviet economy, more directly linked to the Reagan administration sanctions, is to develop a domestic substitute for the General Electric turbine.
At first, the Soviets demonstratively shrugged off Washington's move to embargo the 25-megawatt machine, the unrivaled world-market leader in powering high-capacity pipelines. Within days of Mr. Reagan's June sanctions, the Soviets , whose domestic pipeline workhorse is a less reliable and efficient 10-megawatt turbine, announced the successful preliminary testing of a new 25-megawatt model by a factory in Leningrad.
Yet amid generally glowing reports of progress in the development and production of the turbine, which is deemed in some ways superior to the GE machine, there have been increasing indications of the sacrifices involved in building the Soviet competitor and of potential problems with the program.
At least 20 Leningrad factories, according to Soviet news media reports, have been pooled into a ''research and production association'' to ensure sufficient quality and quantity in production of the new turbine. Some 10 Leningrad steel mills, according to one brief Soviet report, are included.
A ''special gas pipeline'' is even being laid on the floor of Leningrad's Neva River to allow for testing of the 25-megawatt prototypes.
Further Soviet reports said the Leningrad turbine would replace the planned GE unit in all the compressor stations along the new line. State television said the first Soviet replacement, in an initial batch of nine, would be delivered to its pipeline site sometime in October, several months ahead of schedule. A separate media report said the blueprints of the first compressor station for the line had been redrawn around the Leningrad prototype.
But foreign business sources here, including one who says he has seen factory diagrams of the Leningrad machine, remained skeptical that the Soviets would produce a turbine of GE standard and power in sufficient quantity to meet the pipeline construction schedule.
Soviet media reports, meanwhile, have reinforced this skepticism by mentioning production of at least three other Soviet turbines for the Siberia-West Europe pipeline. One of them is a 10-megawatt model. Five units are said already to have been delivered for use on the new line. A more powerful unit was being designed at the same factory, the report said, and would be produced starting in 1983.
The other new models mentioned are patterned on Soviet aircraft turbines, which, foreign analysts say, is likely to make them less powerful than the GE 25 -megawatt model and less efficient for use in gas-compressor stations.
Further muddying the picture, a Soviet newspaper Sept. 9 reported that a group of unspecified factories had committed itself to speeding production of '' 16- and 25-megawatt'' turbines for use on the new export pipeline.
''My guess,'' said a West European diplomat following the pipeline issue, ''is that even the Soviets have not finally settled on what turbines will go where. . . .''
At present the crucial rotor blade for the GE turbine is produced only in the US. With current stocks of rotors in Europe, companies defying the Reagan sanctions could provide an estimated total of 40 or so completed turbines. The pipeline design calls for three 25-megawatt machines per compressor station, leaving a deficit of roughly two-thirds of the initial order of GE turbines for Moscow to fill.
Given the Kremlin's record of commercial pragmatism, most diplomats suspect the Soviets will resist the political temptation to assemble all-domestic compressor stations and make use of any embargo-busting turbine deliveries that materialize.
For the rest, the Soviets presumably will rely on the most efficient mix from what is clearly a crash program to produce more powerful and efficient domestic turbines for the line.
A Soviet foreign-trade expert, interviewed by the Monitor Sept. 8, stressed that the West should have ''no doubts'' that Moscow has the technological and other resources to meet this challenge.
He argued that US economic pressure will not work - a statement with which virtually all diplomats here agree, in the sense that Reagan pipeline sanctions are not likely to secure the announced aim of loosening martial law next door in Poland.
Yet the Soviet analyst declared that Moscow, like any other commercial partner on any other project, had contracted for GE turbines to save ''time and resources.'' As such, countering the Reagan sanctions on the turbines produces inescapable constraints on both fronts, he said.