Snam, controlled by state lender Cassa Depositi e Prestiti (CDP), has a strategic alliance with Belgium's Fluxys as it seeks to expand its footprint across Europe.
The company's strategy is in step with long-running government plans to cut high energy prices by transforming Italy into a southern European gas hub with supplies from Russia, North Africa and, further down the road, Azerbaijan.
In its four-year business plan to 2017, Snam announced it had signed a memorandum of understanding with CDP to buy its 89 percent stake in TAG.
The 400-km (250-mile) pipeline, 11 percent owned by Austria's OMV, has long been seen as strategic by Italy in bringing in Russian gas through Ukraine, Slovakia and Austria.
Italy, which imports around 90 percent of its gas needs, has become increasingly dependent on Russian gas after oil major Eni agreed last year to take lesser volumes from Algeria.
Eni Chief Executive Paolo Scaroni has said any gas crisis stemming from the growing dispute between Russia and Ukraine over Crimea would not for the time being threaten Italy's energy needs but added if another gas source, other than Russia, went down the problems would be serious.
"The (TAG) acquisition, likely to be done through a capital increase reserved for CDP, will not only help boost capital but will also boost earnings by 3-4 percent and support dividend policy," Societe Generale utility analyst Alberto Ponti said.
Snam CEO Carlo Malacarne previously said that to buy TAG the group may issue new shares for CDP, which bought the pipeline in 2011 for 710 million euros ($988 million), including debt.
Snam's four-year business plan did not disclose any figures for the size of the deal or when it would be completed.
CDP owns 30 percent of Snam, which gives it a controlling grip on shareholder meetings. It is currently looking for a buyer, or buyers, for a stake of up to 49 percent in the vehicle which controls Snam and which could soon also control a similar stake in power grid operator Terna.
Snam - which operates regulated gas transport, distribution and storage assets - said it planned to invest 6 billion euros to 2017 to develop the Italian gas grid "with a view to promoting the true interconnection of European networks".
In its previous plan, the gas transport group had earmarked investments of 6.9 billion euros but that included about 700 million euros to buy a French gas network in a deal completed in 2013.
Gas demand in Italy has fallen by more than 15 percent since 2008 due to poor industrial production in a prolonged economic recession.
Snam also said it would offer a dividend of 0.25 euros per share both this year and next, in line with last year's dividend. It said it would pay the dividend once a year and would not offer an interim payment.
"Some analysts had been concerned the dividend could be cut so that's good news, though what has raised a few eyebrows is that they've only given visibility out to 2015," Ponti said.
An interim regulatory review for the core business of transmission and distribution is expected in 2016 and some analysts are concerned that falling Italian interest rates could affect returns.
As a regulated business Snam has its returns set by the energy regulator which takes account of sovereign bond yields.
Snam shares were down 0.8 percent at 1048 GMT while the European utility index was down 0.2 percent. ($1 = 0.7188 euros)