Party chief Sonia Gandhi chaired a meeting of the subjects committee to finalise the political, economic and foreign affairs resolutions which will be moved and adopted during the three-day event.
Party sources said the political resolution will lay stress on the Congress being "the only national party which has a pan-India existence".
It will also touch on issues of probity in public life and the internal security challenges facing the country.
According to sources, some members suggested that the links of right-wing Hindu groups, like the Rashtriya Swayamsevak Sangh (RSS), with terror should be "seriously investigated".
Prime Minister Manmohan Singh attended the meeting, which lasted almost four hours, along with senior leaders, including Finance Minister Pranab Mukherjee, Defence Minister A.K. Antony and party treasurer Motilal Vora, at the Parliament House Annexe here.
The sources said that Congress members from Kerala, West Bengal and Tripura wanted that the resolution should not talk of the Left parties "as other opposition parties" but name them specifically. Kerala and West Bengal face assembly polls next year and Left parties are the main political rivals of the Congress in these two states.
The sources said the resolution will also discuss the role of the Congress in various states.
"The emphasis would be to project the Congress as a national party which also caters to regional aspirations," a senior Congress leader told IANS.
Party sources said the 2G spectrum controversy is expected to find a mention in the context of probity in public life. The party is also to mount an attack on the Bharatiya Janata Party (BJP) for not taking decisive steps in Karnataka despite allegations of nepotism against state Chief Minister B.S. Yeddyurappa.
The situation in Jammu and Kashmir, cross-border terrorism and threat of Maoist violence are also likely to find a mention in the political resolution.
It is expected to mention the achievements of the first United Progressive Alliance (UPA) government and the tasks ahead of the present government.
The sources said that the resolution on the Congress completing 125 years will trace the party’s history and is likely to mention the contributions of Mahatma Gandhi and earlier prime ministers Jawaharlal Nehru, Indira Gandhi, Rajiv Gandhi and party president Sonia Gandhi.
While the economic resolution is expected to emphasise inclusive growth, the foreign affairs resolution will speak about the growing role of India in the global affairs, party leaders said.
The next two days of the three-day plenary session will be held at a sprawling tented township in Burari in northwest Delhi and is expected to be attended by 1,250 All India Congress Committee (AICC) delegates and around 15,000 other leaders and party activists.
The Delhi plenary is being held at a time when the Congress-led government is facing a series of corruption scandals and controversies.
While the political resolution and the statement marking the culmination of 125 years of the party are expected to be moved on Sunday, the economic and foreign affairs resolutions are likely to be moved Monday.
Gandhi will set the tone of the deliberations in her presidential address Sunday morning.
Delhi is hosting the Congress plenary for the first time in 32 years. Indira Gandhi, then in the opposition, presided over the last session in Delhi in 1978.
The Subjects Committee includes members of the party steering committee or the working committee, chief ministers, state Congress chiefs and Congress legislature party leaders.