* Belgium considering British, U.S. fighter jet proposals
* French proposal not part of tender process
* Belgium says checking legality of French offer
* Tender decision due next year
BRUSSELS, Oct 5 (Reuters) - Belgium has received proposals from Britain and the United States to replace its ageing fleet of fighter jets, while a French proposal that was not part of the tender process will be looked at separately, Belgium's defence minister said.
Belgium invited government-led proposals in March for the replacement of its fleet of Lockheed Martin F-16 planes with 34 new fighters, in a deal that could be worth more than 3.5 billion euros ($4.2 billion).
Last month, France proposed a wide-ranging military deal with Belgium instead of responding to the tender. The deal goes beyond the terms of the tender whilst including the sale of Rafale fighter jets.
While the French offer would be discussed by the government, it could open Belgium to criticism that it was not treating candidates equally, Vandeput said.
"To be very clear, the French offer is not part of the contest," minister Steven Vandeput told a parliamentary committee on Wednesday.
Offers from the U.S. for Lockheed F-35 Lightning II planes and British offers for the Eurofighter Typhoon did meet the tender rules, the minister added.
A spokeswoman for the defence ministry said the French proposal was being checked by its legal services and forwarded to the government which would decide at a later stage whether or not to respond.
The Rafales are made by France's Dassault Aviation which declined to comment on Thursday.
Boeing pulled out of the race last spring.
The French government said that its proposal was in line with Belgium's request.
"We have made an extended proposal which is legally relevant and we are waiting for a proposal by the Belgian government," a spokeswoman for the French defence ministry said.
Belgium will make a decision on which jet fighter to pick next year.
The 34 jets are to be delivered from 2023, at a rate of 4-5 aircraft a year.
$1 = 0.8498 euros Reporting by Robert-Jan Bartunek and Cyril Altmeyer; Editing by Elaine Hardcastle