Rep. John B. Anderson (R-Ill.) said yesterday that expansion of federal financing from presidential to congressional elections will face a difficult time on Capitol Hill because incumbents are not likely to change the system that helps keep them in office.

Anderson, who with others is drafting a bill to permit federal matching funds in congressional elections, made his remarks yesterday during the first day of a two-day forum on the election process. The National Broadcasting Co. is conducting the forum.

At a morning session, Rep. Morris K. Udall (D-Ariz.) outlined changes he would like to see enacted by law in the presidential primary system. Udall, who failed to win any of the 22 primaries he entered in 1976, called for limiting state primaries to four primary dates, one each month beginning in March of an election year.

Udall's proposal would permit a state to choose which of the four dates it wanted for its primary, and active candidates would be required to enter all the ones held on a specific date rather than pick and choose among states as is now permitted.

The Anderson plan for federal financing and the Udall proposal for primaries drew support and opposition from the politicians, academics and journalists attending the sessions.

Former Sen. Bill Brock (R-Tenn.) chairman of the Republican National Committee, warned that it was "dangerous to establish national standards" for primaries and said each state should be allowed to evaluate the process for itself.

Sen. John G. Tower (R.Tex.) attacked the concept of federal money in congressional campaigns on the grounds that it would lead to "inordinate government intrusion." To Anderson's claim that special interests have become the basic financers of Congress, Tower responded, "That is sheer bunk and baloney."

John Sears, manager of Ronald Reagan's 1976 presidential campaign, said politicians want to tinker so few people participate in elections. Not totally tongue-in-cheek, Sears proposed the best solution to that problem would be to pass a law requiring every eligible citizen to vote in primaries and general elections.