President Reagan's social issues offensive of the last two weeks has increased the nervousness with which some of his advisers are approaching the midterm elections.

The concern centers on Reagan's high-visibility involvement in the right-to-life issue, on which the president is deeply committed to the anti-abortion cause. Reagan's stand on behalf of the anti-abortion amendment defeated in the Senate last week was expected, both because of his own beliefs on the issue and promises he had made to human rights groups.

What was not anticipated was that the president would refer to it in three separate speeches -- including a session with religious editors in which Reagan was supposed to talk about tuition tax credits. This was the speech in which Reagan asserted, contrary to any evidence yet discovered, that babies have been born prematurely at three months and grown to be normal adults.

Polls taken for the White House show what other surveys have found: that two-thirds of respondents oppose a constitutional amendment or federal legislation prohibiting abortion.

"The issue just ruins us whenever it comes up," says one administration official who hopes it does not come up very often. He got his wish Friday, at least, when Reagan made no mention of the abortion issue during his New Jersey campaigning.

Reagan's preferred issue for October is the economy, about which the president is genuinely and typically optimistic. This optimism isn't shared by several of his advisers, some of whom privately express a deep and developing pessimism about the probable impact of September unemployment figures on the midterm elections.

This pessimism is focused on Oct. 8, the date when September jobless figures, the last issued before the Nov. 2 general election, are released.

These figures are expected to show that unemployment has reached 10 percent for the first time since the Great Depression, in the days when Reagan was a New Deal Democrat and Franklin D. Roosevelt was his political idol.

While a case can be made that a 10 percent unemployment figure today is not what it used to be because of the number of families with more than one breadwinner and the expansion of insurance and social welfare programs, the political consequences of reaching this figure could be immense.

"It's a psychological barrier that we don't want to break," an administration official acknowledged last week.

The White House is working hard behind the scenes to convert Rep. James D. Santini, the Nevada "Boll Weevil" Democrat who narrowly lost his state's Senate primary to incumbent Howard W. Cannon, to the Republican Party.

One scenario has Santini coming out for GOP nominee Chic Hecht in return for what one Republican close to the White House described as "a suitable future reward."

Sen. Paul Laxalt, the Nevada Republican who is Reagan's closest intimate in Congress, doubts the conversion will occur, pointing out that Santini had an opportunity to change parties last year with the almost certain likelihood of gaining the GOP nomination in the process.

Santini chose to remain a Democrat and run against Cannon.

With or without Santini, Laxalt believes that Hecht, who was minority leader of the state Senate when Laxalt was governor and is a close personal friend, has a strong chance.

"He's got a good shot. Reagan remains terribly popular out there, and Hecht is a good candidate who will get the money he needs," Laxalt says.

Hecht will also get help from Reagan, who will campaign in Nevada Oct. 11 after another political stopover in New Mexico and three days at his beloved ranch in the Santa Ynez Mountains north of Santa Barbara, Calif.

Reagan has postponed an Ohio political trip Tuesday so he can appear at a $500-a-person reception here for David Emory, the Republican Senate candidate in Maine. "Emory's chances will be greatly helped if he gets the money now rather than later," says one White House official.

In an event so badly timed for the Reagan administration that one official privately calls it "an embarrassment," the Young Americans for Freedom will sponsor a $50-a-plate "Tribute to Raymond J. Donovan" dinner Oct. 13.

The list of sponsors include White House powers such as counselor Edwin Meese III and some former ones such as ex-national security adviser Richard V. Allen.

Not included is White House Chief of Staff James A. Baker III, who said dryly that he didn't recall being asked and would be "happy to serve" as a sponsor.

Two comments, one of them anonymous, sum up the division on Donovan. One is from an administration official critical of the political cost of keeping the oft-investigated secretary of labor. "It will be interesting to see how many of the sponsors show up," this official said.

But Donovan is now becoming something of a conservative celebrity. Sam Pimm, a member of the dinner committee and YAF official, was quoted as saying: "He is really one of the most popular members of the Cabinet among the Young Americans for Freedom."