Former Senate majority leader Howard H. Baker Jr. (R-Tenn.) said yesterday that presidential elections are too long and expensive and called for a ban on political contributions by political action committees and labor unions.

He contended that the long campaigns contributed to the "tragedy" of low turnout in U.S. elections, and he advocated trying to prevent candidates from beginning their campaigns more than a year before the election by not allowing the federal government to match funds raised before Jan. 1 of an election year.

Baker testified at the first meeting of the Commission on National Elections, a bipartisan study panel sponsored by the Georgetown University Center for Strategic and International Studies, which plans to make a report this year.

It is co-chaired by former Democratic National Committee chairman Robert S. Strauss and former representative (later defense secretary) Melvin R. Laird (R-Wis.) and includes Sens. Wendell H. Ford (D-Ken.), John Heinz (R-Pa.) and Charles McC. Mathias Jr. (R-Md.); Reps. Tony Coelho (D-Calif.) and Guy Vander Jagt (R-Mich.), chairmen of the Democratic and Republican congressional campaign committees; Katharine Graham, chairman of the board of The Washington Post Co., and Lane Kirkland, president of the AFL-CIO.

Baker, who retired from the Senate last year, said that he wanted to be president but that he wouldn't make his decision about running in 1988 until after the 1986 elections.

He said independent campaigns by political action committees are a "real problem" and a "legal charade." The Supreme Court ruled Monday that two conservative political action committees could spend unlimited amounts on independent campaigns on behalf of nominees.