Washington — A Reagan administration effort to clamp down on lobbying by federal contractors has inspired one of the oddest coalitions in recent times. Defense contracting giants such as Lockheed Corporation and Ford Motor Company find themselves next to religious charities and the Urban League in a protest against stringent new rules proposed by the Office of Management and Budget (OMB).
''We're catching it from all sides,'' says Michael Horowitz, chief counsel to OMB director David A. Stockman.
Ironically, the new restrictions are seen by the New Right as a way to cut off federal dollars flowing to ''liberal'' groups such as Planned Parenthood. But since the rules were unveiled late last month, the loudest objections are coming from President Reagan's own allies, industry and business.
At a White House meeting with Mr. Horowitz last week, a group of Washington representatives of major corporations ''protested vehemently,'' says Gary Lipkin , assistant general counsel for the National Association of Manufacturers (NAM).
''There was an expression of disbelief,'' Mr. Lipkin recalls. The message the group delivered, according to the NAM lawyer, was, ''We've helped you in times past. We've gone to the well for you when we backed the (1982) tax increase. After all these favors, look what you're doing to us.''
As proposed, the new lobbying ban would go far beyond existing prohibitions. Most groups that receive federal funds would have to set up separate offices to conduct political advocacy, even to file a ''friend of the court'' brief in a government case.
Under the rules, a copying machine used in a government contract could not be used in off-hours to copy letters to Congress.
The regulations would permit a group's headquarters to house some political advocacy - but only if it takes up no more than 5 percent of the total office. Otherwise, a separate facility would be required.
Since virtually every major corporation and nonprofit group, from Ford Motor Company to the Girl Scouts, has some political activity and often some government funding, the proposed rules would have far-reaching effects.
Employees of these groups now keep time records and are subject to audit if they work for both government and privately sponsored projects. Staff and equipment can be applied to political activity as long as it is not on federal government time.
The OMB's Horowitz says that with so many groups even the current laws are ''difficult to police.''
Moreover, he charges, ''some groups tell us 'we think the lobbying we're doing is good, and we can't afford it unless we have federal dollars.' ''
Among those applauding the new rules is Richard Viguerie, a leader of the political New Right and publisher of the magazine Conservative Digest. ''The concept is that just about all conservatives feel it's wrong, unfair, and immoral for taxpayers to have to fund liberal activist groups,'' he says.
Mr. Viguerie has been pressuring the Reagan administration to cut off funds to groups such as Planned Parenthood, which operates family planning services for the government. He opposes the group ''because they are advocating abortion, '' and ''because they are an activist, liberal organization.''
Horowitz denies any political motivation in the new rules. ''We do now and have always rejected the notion that we should deny a right to compete for contracts because of political advocacy,'' he says. ''The test should be who could perform the grant or service.''
Private groups insist that the new rules would have a ''chilling'' effect that would deny them a right to speak out.
''He (Horowitz) is telling us what we can't do with our private funds,'' says Nan Aron, executive director of the Alliance for Justice, an umbrella group including environmentalists, consumer advocates, and women's rights groups. She points out that with recent budget cuts, few of those groups have any federal dollars.
''It'll virtually shut down lobbying by organizations that receive federal funds,'' says Robert Smucker, vice-president of Independent Sector, a group of 450 charity funds. Members range from the Red Cross to the National Conference of Catholic Charities and the Rockefeller Foundation.
Opponents of the Horowitz regulations are now concentrating their efforts on the White House. Next they will go to Congress where Rep. John D. Dingell (D) of Michigan has set a tentative hearing Feb. 28 on the OMB proposal. If all else fails, the groups are threatening to take their argument to court, charging denial of free expression.
Horowitz, meanwhile, is promising to hear all comments.