President Reagan yesterday reiterated his commitment to veto any attempt to repeal the 10 percent income tax cut scheduled for this July.

Speaking in his regular Saturday radio broadcast, Reagan also said he would veto any bill to undo indexation of income taxes, which is supposed to prevent inflation from pushing taxpayers into higher tax brackets. (Friday five moderate Senate Republicans--enough to shift the Senate's balance of power--proposed killing indexation, which is scheduled to take effect in 1985, and canceling the third year of Reagan's tax cut program.)

"We will not reverse our progress in reducing tax rates," the president said in his broadcast from Camp David, Md. "We have only begun."

Larry Speakes, the president's spokesman, said despite the defection of the key Republicans on the administration's tax proposals Reagan remains "locked in concrete on that one."

However, the White House is attempting to display new flexibility on the amount of an increase it will accept in defense spending for the fiscal 1984 budget. Speakes said the administration is trying to reopen negotiations with Senate Republicans on the 5 percent boost--half the amount the president requested--voted by the Senate Budget Committee last week.

Meanwhile, the White House announced yesterday that the president will receive the report of his MX commission Monday.

The president will not respond to the report, according to White House officials, until the following week to avoid appearing hawkish before this week's House vote on the nuclear freeze resolution.

Instead, the administration is making plans for a bipartisan ceremony when the president signs the Social Security rescue legislation Wednesday.

The Reagans are hosting Secretary of State George P. Shultz and his wife at Camp David this weekend for informal discussions on subjects ranging from Latin America to the Mideast.

Throughout his speech yesterday Reagan attacked high taxes.

"Here in America, land of opportunity," he said, "governments at all levels are taxing away 40 percent of our nation's income. We've been creeping closer to socialism, a system that someone once said works only in heaven, where it isn't needed, and in hell, where they've already got it."

Later, after detailing his efforts to cut taxes with child-care tax credits, reduced estate taxes and doubling the annual contribution limit on personal retirement accounts, Reagan added: "For all of you who worked hard to meet your tax obligations this year, be on guard. The liberal Democrats in the House of Representatives want you to pay more--much more."

Rep. Paul Simon of Illinois, responding for the Democrats to the president, said Reagan's tax plans would simply shift taxes from federal to local governments. He added that Reagan's policies have resulted in increased numbers of poor people and have raised business failures to the "highest point since the Great Depression.