Manchester, N.H. — Two sets of numbers have caught the eye of Republicans who are planning strategy for the reelection ofRonald Reagan:
* Nationwide, the President now gets a 57 percent approval rating, one of his best ever, according to the most recent Gallup poll.
* In Iowa, where eight Democratic candidates were pounding the President's record for months, Mr. Reagan's approval rating has fallen to 40 percent, his lowest mark ever in the Hawkeye State.
The sharp drop in Iowa has warned the Republican Party that the Democrats are spotting Reagan's weak points - and turning public opinion against him.
That could mean trouble ahead, unless the GOP can counter the hoopla surrounding the Democratic caucuses and primaries as they move from Iowa to New Hampshire, and then to the South and across the rest of the nation.
Some of that counterattack could be seen here over the weekend. A galaxy of high-level Republicans barnstormed the state for two days as New Hampshire prepared to vote on Tuesday.
There was also an unexpected development that could pump added excitement to Tuesday's vote. Democrats are being urged by the state's most powerful newspaper, the Manchester Union-Leader, to cast write-in votes for Mr. Reagan in the Democratic primary.
The effort, sponsored by New Hampshire Democrat Bob Philbrick and the Washington-based Fund for a Conservative Majority, does not have the support of the Reagan-Bush campaign. But the Reagan team is watching it with keen interest.
The Republican leaders stumping the state here this weekend for the President included Senate majority leader Howard H. Baker, Sen. Robert Dole, Transportation Secretary Elizabeth Hanford Dole, and Health and Human Services Secretary Margaret Heckler.
Officially, they were here to boost the vote for the President in the Republican primary. Unofficially, according to well-placed Republicans, they were here for ''damage control'' as the Democrats continued to use Mr. Reagan as their whipping boy in speech after speech.
What are Reagan's weak points? Where are the Democrats hurting him most? You didn't need a pollster to figure it out. You could just listen to the Republicans who came here to speak in favor of his record.
Secretary Heckler made a forceful defense of the President at a downtown Manchester mall. About 100 people were coaxed with free hot dogs, soft drinks, and live country music to attend the rally, despite a cold rain that was falling. The highlights:
Fairness. Mrs. Heckler noted that Reagan is budgeting $318 billion this year for Health and Human Services, which she called ''the people's department - the largest Cabinet post.'' She argued: ''We are taking care of the people.''
Women. ''I'm also proud to be one of the women in this Cabinet,'' Mrs. Heckler said. ''There are three women in the President's Cabinet for the first time in history. And I would say they are independent-minded and outspoken, candid, and perhaps all 'hecklers' as I am.''
Senior citizens. ''I can well remember that just a few years ago, the scare tactics were being used on the senior citizens of America on . . . social security. The President was pivotal in bringing the social security system from the brink of bankruptcy.'' With Reagan's help, social security will now be ''secure for the next 75 years.''
Economy. The Reagan record includes reducing inflation to 3.8 percent and creating 4 million new jobs in the past year. ''Whoever talks about Reaganomics any more? Why should they, because it's worked so well it's no longer a good political issue for the opposition.''
National pride. Americans have begun to have pride in themselves again, she noted. ''We have a natural, positive, strong, courageous leader . . . at the helm.''
The secretary, however, skirted three other issues that have been serving the Democrats well: Lebanon, arms control, and budget deficits.
Lebanon, the GOP hopes, will be a distant memory by the time voters go to the polls in eight months. It's an obvious setback for the President.
Arms control, in the hands of Walter Mondale, Alan Cranston, and others, has stayed at the forefront of the Democratic agenda. The ''nuclear war'' issue has proved especially useful for Democrats among women voters.
Budget deficits - along with the fairness issue - appear to be the major domestic areas hurting the President. In Iowa, even Republicans disapprove of the President's handling of the 1985 budget by a more than 3-to-2 margin, according to the Iowa Poll. Among all Iowa voters, Reagan's budget is rejected by more than 3 to 1.
It will be Republican strategy to turn the deficit issue around on the Democrats, especially if the nomination goes to Mr. Mondale, on whom they hope to pin the ''big spender'' label.
One could see the kind of strategy that might be expected against Mondale in a speech here by another visiting Republican, Rep. Vin Weber of Mondale's own state of Minnesota. Said Mr. Weber:
''Just think about the kind of government that Mr. Mondale and his political party have given my home state of Minnesota. We have the highest personal income taxes in the nation, we have a 6 percent sales tax, we have the highest gasoline taxes in the nation. . . . That's the kind of government Mr. Mondale wants to give this country.''