President Reagan yesterday vetoed a major civil rights bill and sought to avert an expected congressional override vote by presenting an alternative measure that he said would "ensure equality of opportunity for all Americans while preserving their basic freedoms from governmental interference and control."

Reagan, as expected, refused to sign into law the Civil Rights Restoration Act, designed to undo the effects of the Supreme Court's 1984 decision in Grove City College v. Bell.

He said he supported overturning the decision but that the measure approved by Congress would "vastly and unjustifiably expand the power of the federal government over the decisions and affairs of private organizations, such as churches and synagogues, farms, businesses and state and local governments. In the process, it would place at risk such cherished values as religious liberty."

In the Grove City case, the court severely restricted the reach of antidiscrimination laws prohibiting recipients of federal aid from discriminating against minorities, women, disabled people and the elderly, ruling 6 to 3 that the laws cover only the specific "program or activity" that receives the federal funds, not the entire institution.

For example, if a college's science department received federal research grants, but its English department did not, the federal law prohibiting educational institutions from discriminating on the basis of sex would apply only to the science department and not cover discrimination in the English department.

Capping a four-year struggle by civil rights groups to overturn Grove City and ignoring threats of a veto, the Senate approved the measure 75 to 14 on Jan. 28 and the House followed March 2 with a 315-to-98 vote.

Both votes exceeded the two-thirds necessary to enact the legislation over the president's veto, and the Senate was described by leaders of both parties as likely to vote to override today. A House vote to override is expected to follow swiftly.

Republicans were described as being caught in a particularly difficult position during an election year, torn between defying a president of their own party and angering constituencies with a stake in the legislation that he vetoed.

Sen. Thad Cochran (Miss.), a member of the Senate Republican leadership, said a nose count early yesterday indicated the administration was 10 votes short of the 34 that would be required to sustain the veto in the Senate.

Cochran and others said some Republicans may be persuaded by the administration alternative to vote to sustain the veto, but most expressed doubt that it would be enough to reverse the tide in either chamber.

"I think they'd have quite a tough job" switching enough votes to sustain the veto, said Sen. John H. Chafee (R.I.), another member of the Republican leadership.

"There is a chance {for the veto to be sustained}, but it is remote," said Sen. Orrin G. Hatch (R-Utah), a leading opponent of the bill in the Senate. "It's difficult . . . they're pretty dug in," said an administration official.

A spokesman for Vice President Bush said he had no comment on the veto.

House Speaker Jim Wright (D-Tex.) said he was "confident that the Senate and House will move swiftly to override this unforunate and shortsighted veto."

Reagan "may want to turn the clock back on civil rights, but the American people do not," Wright said.

Even before Reagan vetoed the bill, Sen. Edward M. Kennedy (D-Mass.) lashed out at the anticipated veto in a speech on the Senate floor, calling it a "kick in the teeth of civil rights" and describing the president's alternative as a "sham" that would open "gaping new loopholes" in civil rights laws.

The alternative Reagan offered would exempt educational institutions "closely identified with religious organizations" from the federal law prohibiting educational institutions from discriminating on the basis of sex. Current law and the measure approved by Congress exempt only institutions controlled by a religious group, and both chambers defeated amendments on the issue.

In addition, the administration bill would limit coverage of churches and synagogues that receive federal aid to the specific program receiving the money and of religious school systems to the specific school that gets federal funds.

Reagan said those changes were necessary because the "bill presented to me would diminish substantially the freedom and independence of religious institutions in our society." The U.S. Catholic Conference, the National Council of Churches, the American Jewish Congress and other religious organizations had urged Reagan to sign the bill.

Reagan's proposal also would reduce the impact on business and local government.