In the last major poll, Modi's Bharatiya Janata Party (BJP) and its allies are forecast to win 38 percent of votes, news channel CNN-IBN and Lokniti at the Centre for the Study of Developing Societies said.
Another private news channel NDVT forecast a 32.9 percent vote share for the BJP and its alliance partners.
A BJP victory could have repercussions for Indian foreign policy. Aides of Modi, a Hindu nationalist, have said that if he becomes prime minister India will take a tougher line in territorial disputes with China and in its old rivalry with Pakistan.
The last phase of voting will end on May 12 and results are due on May 16.
The CNN-IBN and Lokniti poll gave 234 to 246 seats to the BJP combine -- the National Democratic Alliance (NDA), while NDTV has forecast 259 seats for the NDA.
The ruling Congress-led United Progress Alliance (UPA) is expected to win 28 percent of votes, entitling them to between 111 and 123 seats, according to the CNN-IBN and Lokniti poll. The NDTV survey gives Prime Minister Manmohan Singh's UPA 26.9 percent of votes, resulting in 123 seats in parliament.
The forecasts bring the NDA within striking distance of forming the next government by reaching the halfway mark of 272 in 543 parliamentary constituencies.
Both surveys covered more than 300 constituencies. While the NDTV poll has a margin of error of plus or minus 2 percent, the CNN-IBN and Lokniti survey does not cite a margin of error for its results.
Modi, who has presided over rapid economic growth during more than 12 years as the chief minister of Gujarat state, has been wooing voters by pointing to his track record as a leader who cuts red tape and attracts investment.
Singh's government has been hampered by its economic record, particularly its failure to tackle rising prices and falling economic growth.
India's retail inflation has remained near 10 percent for the last three years, mainly driven by higher food prices. Growth has struggled at a decade-low of nearly 5 percent.
But Modi's image remains tarnished by communal riots in Gujarat 12 years ago when more than 1,000 people were killed, most of them Muslims.