WASHINGTON (AP) _ Sen. William Cohen thought Maine's spuds were getting spurned. Jesse Helms doesn't like the idea of a ''militant activist mean lesbian'' at the Department of Housing and Urban Development.

Different problems, to be sure. But their solutions are the same.

They put up an invisible stop sign, a courtesy known and revered among senators as a ''hold.''

And thus proved, once again, that the art of stalling in the Senate is so highly evolved it's a stiletto in the hands of the skillful.

Cohen held up five of President Clinton's nominations for Agriculture Department jobs because he wanted the government to pay more attention to his potato farmers. Agriculture Secretary Mike Espy, desperate to get his top staff in place, came through with some promises and Cohen relented.

Helms doesn't want anything from HUD other than to get rid of Roberta Achtenberg. A San Francisco city supervisor, Achtenberg is Clinton's choice to head the government's fair housing section.

The conservative North Carolina senator can't see it.

''She's a militant activist mean lesbian, working her whole career to advance the homosexual agenda,'' Helms said. ''She believes that the Boy Scouts of America are a threat to the children of America'' because it won't let gay men be scoutmasters and its creed refers to God.

''Now you think I'm going to sit still and let her be confirmed by the Senate?'' Helms said.

Actually, the power of a ''hold'' is limited. Helms may not sit still, but he may not be able to block her nomination forever.

Senate Majority Leader George Mitchell, D-Maine, last week threatened to bring all 11 pending nominations - all on hold by various Republicans - before the Senate on Tuesday, courtesies or no.

With literally thousands of nominations to handle, it's just a lot easier if everyone cooperates. Which explains the origin of the current ''hold'' system.

Lyndon Johnson, who was Senate Majority Leader before he became vice president, was a big believer in working out problems with bills in the cloakrooms instead of letting them fester in public. In addition, he was trying to deal with an ever-increasing workload.

Under Johnson's leadership, the Senate began conducting more and more of its business by ''unanimous consent,'' bringing already-negotiated bills to the floor and passing them without the need for lengthy debates and votes.

Johnson would also ''sort of confuse everybody as to what was going on,'' sometimes passing 20 bills in one day, says Senate associate historian Donald Ritchie.

The system worked, and continues to this day.

When the Senate leadership plans to bring a bill to the floor, it puts word out on the ''hotline,'' special Democratic and Republican telephone networks.

If a senator has a problem with a bill or a nomination, he or she sends back word and a ''hold'' is put. Another unwritten rule: the leaders never reveal the holder, though they are free to do so.

Most are done by the opposition party, but not always. Helms, for example, used holds repeatedly in his battles with the Reagan and Bush administrations over foreign policy.

Holds sometimes are handed from one senator to another. In rare cases, they've lasted a year or more. Some bills and nominations die, without ever a Senate debate.

Holds are effective only on relatively small things. For example, an attempt by a single senator to put a secret hold on a Supreme Court nomination would be rejected.

They're bargaining chips, not the whole deal.

''It's not official. It's not in the rules. They don't even say who put the hold on - it's anonymous,'' Ritchie said. Yet, ''the most junior member of the minority party has a great deal of clout.''

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Steven Komarow is the AP's chief congressional correspondent