The two events take place in Sapporo, which still has emergency Covid measures in place.
Organisers said "to reduce the risk of infection" they would restrict "the movement of members of the public".
The Games, delayed a year because of the pandemic, start on 23 July.
Event organisers said they had met police and local government officials to discuss arrangements for the race walk events, which take place on 6 August, and the women's and men's marathons, which take place over the following two days.
In a statement, they added that they would continue to work with local authorities "to ensure a safe and secure Tokyo 2020 Games for all participants and for the citizens of Sapporo and Hokkaido".
Meanwhile, the Kyodo News reported that Japan is likely to extend a quasi state-of-emergency for the greater Tokyo area by a month, and that the opening ceremony may be one of a number of Olympics events to be held without spectators.
The delayed Tokyo Games were already set to be staged without the presence of international fans because of coronavirus restrictions..
Local spectators, however, are still set be allowed to attend, with up to 10,000 Japanese fans permitted to watch events, providing crowds do not exceed 50% of a venue's capacity.
The Paralympic Games are scheduled to take place between 24 August and 5 September.