President Reagan reacted defensively yesterday to a suggestion that he doesn't give enough of his personal income to charity, claiming that he also gives money to individuals that he can't deduct from his taxes.

While the president has been urging wealthy Americans to contribute more of their income to charitable causes, Reagan and his wife, Nancy, in 1980 made charitable contributions totaling $3,089, only 1.4 percent of their adjusted gross income of $227,968. In 1979, the only other year in which the Reagans made their tax returns public, charitable contributions were less than 1 percent of their income of $515,878.

" . . . I realize that some have noticed that there seemed to be a small percentage of deductions for worthwhile causes and that is true," Reagan said at his first news conference of the year. "And I'm afraid it will be true this year because I haven't changed my habits, but I also happen to be someone who believes in tithing--the giving of a tenth."

Reagan, a millionaire, said he had "for a number of years done some of that giving in ways that are not tax deductible with regard to individuals that are being helped." Aides said that on occasion Reagan has sent contributions to people who have written him letters containing hard-luck stories.

But White House deputy press secretary Larry Speakes said that Reagan was not attempting to claim that he gave away one-tenth of his income--or anything close to it--to private individuals.

One-tenth of Reagan's income in 1980, when he spent most of the year campaigning and earned most of his income from interest, would have been $22,797. A tenth of Reagan's income in 1979, a typical pre-campaign year in which the bulk of his income came from speeches, a radio show and a newspaper column, would have totaled $51,588.

Reagan traces his presently unpracticed belief in tithing back to a time 50 years ago when he was a student at Eureka College in Illinois, earning $100 a month. He went to his minister at the college and asked whether he would satisfy the religious requirement of giving a tithe if he sent $10 each month to his brother, who had been working at a cement plant closed down by the Depression. Apart from this instance, Reagan has never claimed--so far as is known--to have actually contributed a tenth of his income to church or charitable causes.

Reagan was responding yesterday to a question about whether he planned to increase his charitable contributions "to set an example to the rich people of this country to do more for the poor." He said he planned to do this, but not until next year.

In response to another personal question, the president said he would be hesitant to approve abortion even if his daughter had been raped. Allowing abortions for this purpose had proved "a gigantic loophole" in the abortion law he signed while governor of California in 1967, he said.

In fact, the loophole in the law, which critics said had permitted "abortion on demand," had nothing to do with the provision permitting abortions in cases of rape or incest. Most of the abortions performed under the law--a point correctly cited by Reagan many times in the past--came under another provision permitting abortions if a doctor says that a woman's mental health would be endangered by having a baby.

California had 518 legal abortions in 1967, the year the measure was enacted. By 1978 the figure had climbed to 171,982 abortions a year and totaled 1,230,359.

Reagan has said on several occasions that he regrets having signed this bill and that he considers any abortion "the taking of a human life," a position he repeated yesterday.