Sunday's House of Representatives election in Japan is likely to deliver a robust victory for Prime Minister Shinzo Abe's Liberal Democratic Party while ending in disappointment for Tokyo Gov. Yuriko Koike's Party of Hope, a Kyodo News survey showed Tuesday.

The LDP and its coalition partner the Komeito party are together projected to win about 310 seats, a two-thirds majority in the 465-seat lower house.

The Constitutional Democratic Party of Japan, formed in recent weeks to take on the liberal wing of the moribund Democratic Party, now has a chance of coming out on top among the opposition parties, ahead of the Party of Hope, which took in the Democratic Party's conservative wing.

But the projections have the potential to change in the campaign's last few days, with some 40 percent of voters still undecided on which candidate or party to vote for.

According to the telephone survey receiving responses from around 120,000 randomly selected eligible voters nationwide conducted between Sunday and Tuesday, an initial burst of excitement over the "reform conservative" Party of Hope appears to have ebbed. It is now projected to win about 50 seats, having slipped in the polls since before campaigning began on Oct. 10.

The CDPJ is on track to win nearly 50 seats, having trebled its support since before the start of the campaign.

Japanese voters get two votes -- one for a candidate in their single-seat electoral district and one for a party. Single-seat districts account for 289 of the seats in the house, while the party votes dictate how the remaining 176 seats will be allocated through 11 regional proportional representation blocks.

Some 40.3 percent of respondents did not specify a preferred candidate, and 40.0 percent did not specify a preferred party.

Three-way lower house election battle heats up in heart of Tokyo

The LDP is forecast to pick up about 220 of the single-seat districts and do better than any other party in the proportional representation seats, giving it a total of about 280 seats, according to the latest survey. The party had 290 seats before the chamber was dissolved.

The lower house had 475 seats before it was dissolved, but shrank by 10 seats to a postwar low of 465 through electoral reforms.

A two-thirds supermajority is significant because Japan's Constitution, reform of which has been the LDP's goal since its inception in 1955, requires at least two-thirds of lawmakers in both Diet houses to approve a proposed amendment before it can be put to a nationwide referendum.

Most major parties are in favor of or open to constitutional amendment but differ on how to handle the war-renouncing Article 9 and other issues.

The Party of Hope has slipped in the polls during the campaign. Its prospects are best in districts where it is fielding candidates hailing from the Democratic Party who held the seats before the lower house was dissolved on Sept. 28.

The party is on the back foot in all of the single-seat districts in Tokyo, despite Koike's popularity in the metropolis.

The Japanese Communist Party is expected to lose ground in the proportional representation vote, with its total seats possibly falling from 21 before the campaign began.

The Osaka-based Japan Innovation Party faces uphill battles against candidates backed by the LDP and the Komeito in some districts in Osaka.

The Social Democratic Party is forecast to put up a fight for two seats, while the tiny conservative Party for Japanese Kokoro may fail to get any, having lost its former leader to the Party of Hope.

Voters' interest in the election has grown slightly over the course of the campaign, with 77.6 percent of respondents saying they are very or somewhat interested, up 3.4 percentage points since just after the start of the campaign and up 6.9 points since the same time in the last lower house election campaign in December 2014.