In a move that sidesteps the federal spending limit in Monday's Iowa presidential caucuses, Rep. Richard A. Gephardt's (D-Mo.) campaign counted only half of nearly $240,000 it spent on television commercials in December toward the limit.

The Gephardt 30-second commercials contained a tag line asking viewers to "volunteer, vote and contribute." Gephardt's campaign attorney, Robert F. Bauer, said yesterday that although the fund-raising appeal was limited to a single word, the campaign is confident it can justify the 50 percent write-off.

He said the Gephardt campaign was low on funds when it decided to advertise on television in the days between the Christmas and New Year holidays, when most voters are thought to be distracted, in an effort to raise money from hard-core Gephardt supporters in Iowa.

Bauer said the campaign patterned its 50 percent fund-raising allocation after a case the Federal Election Commission allowed in the 1984 presidential campaign of Sen. John Glenn (D-Ohio).

FEC spokesman Frederick S. Eiland said yesterday that the Glenn case was decided on a specific set of facts. The Gephardt campaign did not seek an advisory opinion on whether it could take a similar 50 percent write-off for fund-raising, he added. "The tendency {for candidates} is to get as far out on the edge as they can."

If the FEC contests the 50 percent write-off, Bauer said, the potential impact on the Gephardt campaign will be from "$75,000 to $125,000." If that amount must be added to Gephardt's Iowa totals, he could be subject to a fine for violating the state's $775,000 spending ceiling.

Gephardt's heavy television spending for Iowa has been a key factor in his surge in the polls there over the last month.

It also has become an issue in the closing days of the campaign. Sen. Paul Simon's (D-Ill.) campaign manager accused Gephardt of ignoring the limits and said he should take his commercials off the air.

News media interest in Gephardt's treatment of the Iowa spending limit also was heightened because his year-end spending report, which was due to be postmarked Jan. 31, did not arrive at the Federal Election Commission until yesterday.

Gephardt denied he was breaking the limit, and his campaign released copies of the year-end report, which it said was lost in the mail.

The report shows that Gephardt spent $494,175 in Iowa through the end of the year. It shows the media buyer, Doak, Shrum & Associates, made a single television purchase Dec. 9 for $80,709.76. The report also shows that on the same day a purchase of $169,290.24 was listed on a separate schedule of expenditures that the campaign counts as fund-raising costs exempt from spending limits.

Although it appears that Gephardt was writing off two-thirds of his December media spending for fund-raising, Bauer said the campaign actually exempted only half of the December buy.

Bauer said the report mistakenly included $30,000 of exempt production costs in the December buy category, so the television buy allocable to Iowa was really about $112,000.

Only about $125,000 of the $169,290 listed as exempt for fund-raising is allocable to Iowa, he said.

Under FEC rules, a candidate who tries to raise funds with television commercials can write off part of the cost up to 28 days before an election. But the regulations do not say how much.

After the 1984 campaign, FEC auditors rejected an attempt by Glenn to exempt all of a half-hour television show as a fund-raising cost. But they did allow him to write off 50 percent of the costs.

Bauer said he and other Gephardt campaign officials looked carefully at the Glenn audit before deciding "we could draw on substantial documentation to demonstrate the Glenn percentage was one we could use." He said the standard is "a flexible one" and the Gephardt campaign might adjust it in later reports.

Gephardt's campaign manager, Bill Carrick, said the campaign has made "every effort to stay under the cap," adding, "I do not feel our expenditures are as substantial as several of our competitors'. We have not used direct mail. We have not used radio like Paul Simon. And we are nowhere near Dukakis' league in the number of bodies on the ground here."

Massachusetts Gov. Michael S. Dukakis (D) also ran television commercials with fund-raising tags. Leslie Dach, director of communications for the Dukakis campaign, said yesterday he did not know how much of a write-off his candidate took.

Staff writer Dan Balz contributed to this report.