Washington — From President Reagan to Miles Rapoport, politicians are racing to computerize their campaigns. When Reagan reelection officials need information, they can call up PINS. A complex computer data base, PINS (Political Information Systems) answers such crucial questions as ''How are we doing among independent California voters?'' and ''How much money is Walter Mondale spending in Maine?''
When Miles Rapoport wants political advice, he turns to an IBM personal computer. Mr. Rapoport, a candidate for the Connecticut Legislature, uses the computer to identify streets where his support is strong.
All across the country, computers are bringing a new level of sophistication to the business of running for office. Even grass-roots candidates are using computers to decide which voters to contact, who to ask for money - and who to ignore.
''This is the wave of the future. It allows you to run a 21st-century campaign,'' says William Miller, marketing director for Politech, a political software company.
American politics has been relatively slow to embrace computers. A campaign for office is short, fierce, and fluid; and the mainframe computers of years past were too cumbersome and expensive to be of much use to candidates, experts say.
But the explosion in mini- and microcomputers, and ever-better computer communications, has made data processing a useful weapon in political wars. Upwards of 2,500 computer firms now offer politically oriented services; some federal candidates spend 10 percent of their campaign budget on computers.
''Every congressional campaign is using them now, without doubt,'' says Robert Abeshouse, managing editor of Campaigns and Elections magazine.
It is the presidential campaigns, of course, that have the most impressive data-crunching power. Both Mr. Mondale and Mr. Reagan use large mainframes for campaign housekeeping: keeping the books, preparing Federal Election Commission reports, listing names of newly registered voters.
At the Reagan/Bush '84 headquarters there is an added twist: The computer is a useful tool in deciding on daily tactics. PINS provides senior campaign staffers with help at the touch of a keyboard.
PINS, Reagan staff members say, contains enormous files of raw information, such as current economic statistics, opposition spending, and voting patterns in past House races (by county). It also projects election results, based on daily tracking polls, so campaign officials can quickly spot shifts in voter mood.
''For the political realm, (PINS) is very sophisticated,'' says a Reagan campaign staff member who asked not to be named. ''In the business world, a lot of CEOs (chief executive officers) have things like this.''
Senate campaigns also tend to use elaborate computer systems. Take Sen. Jesse Helms (R) of North Carolina, well on his way to becoming the biggest-spending Senate candidate in history. Senator Helms is running an all-Burroughs campaign: His immediate staff uses Burroughs B-20 minicomputers, while one of his campaign's political consultants, Jefferson Marketing, of Raleigh, N.C., has a big Burroughs mainframe.
The campaign's B-20s contain numerous lists of supporters, which are used to target flyers and appeals for cash. ''They like to see how many contributors who did give in the past haven't given recently, stuff like that,'' says Ralph Graw, a Helms B-20 specialist.
The B-20 even holds names of those who support the opposition, Democratic Gov. James B. Hunt Jr. Helms is preparing a mailing designed to win over these opposition voters.
''We did have a problem recently,'' admits Mr. Graw. ''Our computer caught on fire. We came close to losing all our data.''
But it is on lower races (House, state representative, county commissioner) that computers may have their most profound effect. At this level of politics, lists of supporters, with phone numbers, are particularly valuable - and some candidates are using microcomputers to compile these names as never before. Fourteen companies now offer computer software designed for use in small campaigns.
With a small computer and raw data from local election commissions, grass-roots candidates can match phone numbers to names of registered voters. They can determine which precincts have high turnouts of voters from their party. They can even calculate ''fall-off'' - the percentage of voters who vote for the glamor races at the top of the ticket, then leave the rest of their ballot blank.
''Not that many people do this yet,'' says Murray Fishel, a Kent State political scientist who specializes in grass-roots politics. ''But there's going to be a tremendous explosion in lists.''
Miles Rapoport, for instance, is running for the Connecticut Assembly. He and his aides have talked to almost everyone in their Hartford-area district and listed these voters' leanings on an IBM personal computer. With this list, they know who to include in their get-out-the-vote effort - and who to leave out, notes a Rapoport worker.
Mr. Rapoport, a Democrat, defeated the district's incumbent in the primary.
With computers, candidates can divide up voters into numerous categories - blacks, whites, elderly, ''yuppie,'' those who make more than $65,000 a year, lawyers, and others. Mail or flyers can then mention issues of particular interest to the recipient. A few state parties are beginning to build ''libraries'' of such data to aid future candidates. The Nebraska Democratic Committee (NDC) has spent $70,000 on an IBM-36 minicomputer, as the first step toward compiling a comprehensive Voter Information Service.
''If (the state party) is going to be meaningful, we have to offer services to candidates,'' says Marg Slominksi, NDC's director. ''It used to be the only contact we had with them was when they called up to scream we weren't doing anything.''
Ms. Slominski contends that the computerization of campaigns will strengthen political parties. Tapes of data will allow parties to give more help with fund raising, voter registration, vote getting, and other actions. Quick computer communications will tighten ties between candidate and party, she says.
The Republican Congressional Campaign Committee, for example, already has an electronic mail service that can zap out position papers within hours of a politically notable event.
Other experts take issue with Slominski's assertion. ''Computers allow neophyte candidates to run an efficient campaign on their own,'' says William Miller of Politech. ''They won't have to go through the party.''
And there may well be a dark side to the rise of political computers. Computer-targeted mail could allow unscrupulous candidates to present a distorted picture of themselves - saying one thing to union members, another to business leaders, for example. Moreover, computerized voter dossiers can be disturbingly detailed.
''Individual voters can now be identified by all sorts of measures. At some point, a person's privacy is invaded,'' says Larry J. Sabato, a University of Virginia political scientist.