Common Cause accused the National Republican Senatorial Committee (NRSC) yesterday of setting up a $1.4 million "political slush fund" that is being used to finance restaurant bills, makeup for television appearances, office interior decorating, Spanish lessons and a host of other expenses.

An undetermined number of senators may have violated federal tax law by failing to report payment of bills by the fund on their personal tax returns, according to Common Cause. The self-described citizens lobby specifically named three Republican senators, Paula Hawkins (Fla.), Pete Wilson (Calif.) and Chic Hecht (Nev.), who did not report receiving money from the fund to the Internal Revenue Service.

Aides for the three senators referred questions to the NRSC, where legal counsel Jan Baran said there is nothing illegal about the fund. Baran said the payments it makes on behalf of senators are for legitimate expenses and that senators do not need to report the money as taxable income. He compared it to the payment of travel expenses by a corporation for an employe.

Common Cause said a 1980 IRS advisory ruling spelled out the requirement that the money be reported by the senators on their income tax returns, and a spokesman for the IRS, Larry Batdorf, confirmed the assessment made by Common Cause that the money should be reported. The spokesman also said the expenses paid by the fund are deductible by senators who can prove that they covered legitimate expenses.

Baran, told that the IRS disagreed with his opinion, said the natural inclination of the IRS is to treat anything it can as taxable income.

Common Cause, in attacking the special NRSC fund, also raised two other points.

First, some of the expenses apparently fail to meet IRS requirements as "ordinary and necessary" costs of holding office, including restaurant bills, Spanish lessons and interior decorating. "The receipt of this money could have resulted in the payment of additional income taxes by those senators because expenditures were not 'ordinary and necessary,' " Common Cause said.

Secondly, some of the expenses covered by the NRSC fund may be political and therefore should have been reported as campaign contributions to the Federal Election Commission. Common Cause cited the spending of more than $10,000 by Sen. Alfonse M. D'Amato (R-N.Y.) for a firm that maintains voter registration lists and the overall spending by the fund of more than $400,000 for "radio and television tapes and photography services."

The NRSC's special office account fund in 1983-84 channeled $1.4 million to GOP senators and $450,000 during the first eight months of 1985, Common Cause reported. The Democratic Senatorial Campaign Committee does not raise enough money to set up a separate office account for Senate members.

The Republican fund was created in part because the NRSC raises far more money than it can legally spend, directly and indirectly, in support of Republican candidates for the Senate. The excess cash, in this case, has been used to create a fund to pay for such "noncampaign" expenses as newspaper subscriptions and production costs for a wide range of television, newsletter and radio communications with constituents.

Common Cause charged that the fund has been used to pay expenses that could be interpreted as violating IRS regulations. The IRS requires that the money be used for "ordinary and necessary expenses of holding office."

Among the claimed expenses cited by Common Cause as possibly failing to meet the IRS requirement of "ordinary and necessary" were $2,800 spent by Sen. Paul S. Trible Jr. (R-Va.), for a bill from Fourways, a Washington, D.C., restaurant; the costs of Spanish lessons for Wilson; $2,400 for a staff retreat in Williamsburg, Va., for aides to Sen. Warren B. Rudman (R-N.H.); $1,100 for interior decorating for Sen. Slade Gorton (R-Wash.); driving lessons for Sen. John C. Danforth (R-Mo.), and television makeup for Sen. John H. Chafee (R-R.I.).

The amount of fund money involved is $52,000 for Wilson, $33,900 for Hawkins and $27,600 for Hecht, according to Common Cause.

Hawkins issued a statement which read in part:

"Common Cause is calling a slush fund the $33,000 I have used for official business trips back and forth from Florida to Washington. That's not slush. That's doing my job as a senator. How else could I have paid for these trips? My office account isn't large enough and I am not personally wealthy."

A spokesman for Wilson cited Baran's legal views to support the senator's decision not to report the money as income on his taxes.

He said the Spanish lessons were justified as part of an effort to improve communications with the California Hispanic community