* Buying supports before shares go ex-dividend on Wed
* SoftBank rises on news T-Mobile and Sprint close to tentative terms on merger
* PM Abe expected to announce snap election on Monday
By Ayai Tomisawa
TOKYO, Sept 25 (Reuters) - Japan's Nikkei share average rose on Monday morning as a weaker yen lifted exporter shares, while expectations for a snap election continued to support overall sentiment.
With the end of the first half looming on Sept. 30 for a majority of listed companies, the market was also underpinned by investors buying up stocks before they go ex-dividend on Wednesday.
The Nikkei rose 0.6 percent to 20,414.93 by the midday break, after adding 1.9 percent last week and hitting a two-year high of 20,481.27 on the back of strong gains in U.S. stocks and a weakening yen, as well as hopes for a snap election.
Prime Minister Shinzo Abe is expected to announce on Monday a snap election scheduled for next month to take advantage of improved ratings and opposition disarray.
Separately, the Yomiuri newspaper reported that Abe plans to compile a new economic stimulus package of around 2 trillion yen ($17.8 billion) by the end of this year.
"The news report about 2 trillion yen has a limited impact to the market, but expectations that there will be more such stimulus talks before the likely election are supporting the mood," said Hikaru Sato, a senior technical analyst at Daiwa Securities.
Abe is expected to hold a news conference after meeting party executives and will likely put pledges to spend more on education and child care, stay tough on North Korea, and revise the constitution at the forefront of his campaign.
SoftBank Group Corp rose 1.5 percent and was the third most-traded stock by turnover after sources told Reuters that T-Mobile US Inc is close to agreeing tentative terms on a deal to merge with Sprint Corp, a major breakthrough in efforts to merge the third- and fourth-largest U.S. wireless carriers.
SoftBank, which controls Sprint, and other Sprint shareholders will own 40 to 50 percent of the combined company, while T-Mobile majority owner Deutsche Telekom and the T-Mobile shareholders will own a majority, the sources said.
Exporters were steady as the yen weakened 0.4 percent to 112.36 yen per dollar. Keyence Corp soared 2.0 percent, TDK Corp surged 2.7 percent and Advantest Corp climbed 2.0 percent.
The broader Topix gained 0.6 percent to 1,673.69. (Reporting by Ayai Tomisawa; Editing by Eric Meijer)