The Congress, however, alleged that the government was "deliberately delaying" the decision, and the criticism of the previous UPA government on the issue was "not valid".
Modi, in his radio address "Mann Ki Baat", urged ex-servicemen not to believe those who were politicising the issue.
"Interests of the former defence personnel is a matter of faith and expression of patriotism for me," Modi said.
Seeking more time from ex-servicemen, Modi said: "This government, and I repeat, this government will give a solution to OROP."
"I am not talking as a prime minister. For 40 years, this (OROP) question has been persisting. Nothing has happened so far," he added.
He said various departments of the government were working on it, but the issue was very complicated and the 40 years have made it more complicated.
"It is not as simple as we thought, it is complicated, and 40 years have added to the complications. The government is finding ways to make it simple and acceptable to all," said Modi.
"There is no need to give reports in media about every step. I assure you, this government will bring to you a solution on 'One Rank, One Pension'," he said.
Miffed over their long-pending demand of OROP not being met, veterans from the armed forces have said they were ready for a protracted fight with the government and would launch an agitation next month.
Modi stressed that officials in the government were engaged to find a solution to the issue and asked the ex-servicemen not to be swayed by politics.
"I will request all soldiers, those who are trying to politicise the issue, have been playing with you for 40 years... I don't want to take any steps that make the issue more complicated," he said.
"Give me some time, you have been patient for 40 years, give me some time as well, give me a chance to work on it and we will solve all the problems," the prime minister said.
Delhi Congress president Ajay Maken told reporters the government was "deliberately delaying the OROP scheme".
Soon after the prime minister's address, Maken said: "Modi's criticism of the UPA government on the issue is also not valid."
Congress leader Amarinder Singh said: "The prime minister should have announced a date to implement the OROP instead of dishing out vague assurances."
"The prime minister either appears to be ignorant, or is deliberately trying to molly-coddle our 25 lakh ex-servicemen by his mere sweet talk," he added.
In the radio programme, Modi also expressed satisfaction over the recently launched social security schemes, and said he wants to create an "army of poor against poverty".
"Over 8.52 crore people have joined the schemes in just 20 days. This shows people's faith in central government's social uplifting initiatives for them," he said.
The schemes -- Pradhan Mantri Suraksha Bima Yojana, Pradhan Mantri Jeevan Jyoti Bima Yojana and Atal Pension Yojana -- were very important initiatives in the direction of ensuring social security, he added.
He said it was unthinkable of security schemes at a token payment of Re.1 per month.
"The government wants to see the poor self-empowered so that they need not depend on others for self survival."
The prime minister also said yoga has become a catalytic agent to connect the world and was very much relevant in the context of 'Vasudhaiva Kutumbakam' (the world is one family).
Modi appealed to the countrymen to make the International Yoga Day, to be observed on June 21, a success.
He also urged people to become yoga ambassadors and make this important knowledge easily available to the world for the welfare of mankind.
Terming the recently launched DD Kisan Channel "an open university of farmers", Modi said: "There is something for everyone engaged in the agriculture and allied sectors."
The channel has a lot for fishermen as well and they must take maximum advantage from it in modernising their vocation, he said.
Congratulating students who passed the Central Board of Second Education examinations, Modi asked them to pick up the future course of study on the basis of their aptitude.
"The students who have not succeeded in their examinations need not be disheartened and take it as an opportunity to find new avenues," Modi said, adding that "success and failure are a part of life. We can learn a lot from failure also".