Two senators, saying that they want to curb the growing influence of the "rich and powerful" on Congress, have unveiled legislation to establish limited public financing of Senate election campaigns.

Charles McC. Mathias Jr. (R-Md.) and Paul Simon (D-Ill.) said at a news conference that their colleagues privately share their view that the escalating cost of seeking office holds politicians captive to political action committees (PACs).

The proposal, which would not cover Senate primaries or House races, would impose spending limits on candidates opting to receive public money from a voluntary income-tax checkoff like the one used for presidential campaigns.

Participating Senate candidates would be given an amount equal to a state's spending limit, ranging from $500,000 in the least populous states to $5.7 million in California. If a candidate's general-election opponent decided not to accept money from the public fund, the participating candidate would be able to obtain additional public money equal to the amount by which the opponent exceeded the state's limit.

Mathias said that "an imperfect feature" of the legislation is that it would not prevent political action committees from spending independently on behalf of a candidate.

Mathias, who is retiring, estimated that a Senate race in Maryland next year will cost a candidate $4 million, compared with the record $25 million spent in North Carolina by Senate candidates in last year's primary and general elections.

Common Cause, the self-described citizens' lobby, said congressional candidates spent a combined $374 million last year, $136.9 million of it in 33 Senate contests.

Mathias said the public financing bill has a "pretty good" chance of being sent to the floor by the Rules and Administration Committee, which he chairs, but he is making no predictions of success in the full Senate.