House and Senate conferees agreed yesterday on details of a bill lifting the mandatory retirement age from 65 to 70 for the private sector.

Conference Chairman Claude Pepper (D-Fla.) predicted the bill would now clear both houses "within two weeks" and be on the president's desk by the end of March. Carter is expected to sign the measure.

A conference deadlock, which had tied up the bill since last October, was broken yesterday when the Senate agreed to a House provision banning all mandatory retirement based on age for most federal workers.

A compromise was worked out on two other provisions passed by the Senate but not the House. One, an exemption from the bill for tenured professors, was granted only until 1982. An exemption for business executives was limited to top executives whose private pensions would amount to $27,000 a year or more.

The Department of Labor has estimated that about 200,000 persons will elect to stay on the job beyond the age of 65, according to Pepper.

Pepper said he hoped the ban on age-based retirement for federal workers would lead to an end of mandatory retirement of all workers. "We are establishing the federal government as a model employer which will use competence, not age, to determine whether a person should retain a job. This experiment will demonstrate the desirability of a complete ban on mandatory retirement in the private sector," he said.

The bill is a first step in fighting "ageism," Pepper said, "a form of discrimination that belongs in a trinity with racism and sexism."

The mandatory retirement curb passed the House last September by a 359-to-4 vote and the Senate in October by a 88-to-7 vote.