The bad news about the mail situation was delivered through the interoffice mail system.

"Dear Senator," began the letters, in which the 100 members of the U.S. Senate were told how much money was available for the rest of this fiscal year to subsidize the cost of mailing by their offices, a service that members of Congress receive free.

The allocations marked the first time that any limit has been placed on mailing by individual lawmakers.

Based on state populations, the allocations ranged from a high of $688,091 each for California Sens. Alan Cranston (D) and Pete Wilson (R) to a low of $13,284 each for Wyoming Sens. Alan K. Simpson (R) and Malcolm Wallop (R) for the remainder of the fiscal year that ends Sept. 30.

Although that might still seem like a lot for a four-month supply of stamps, it could put a crimp in the style of several senators.

For example, Cranston, who is up for reelection this year, spent a Senate high of $1.6 million for mass mailings during July through September last year, according to a report compiled by the secretary of the Senate.

The new allocations were explained to senators in a letter from Sens. Charles McC. Mathias Jr. (R-Md.), the chairman, and Wendell H. Ford (D-Ky.), ranking minority member, of the Senate Rules Committee. In it, they introduced their colleagues to a new world, one that the Senate created for itself by passing a resolution May 14.

The resolution was an attempt to deal with the skyrocketing cost of congressional mail, which Mathias said had more than tripled since 1978 and which he estimated could reach $146.2 million this year, if not restrained.

The situation was complicated by a recent General Accounting Office ruling that, under legislation enacted by Congress in 1982, whatever Congress appropriates each year for mailing expenses is considered "full payment" to the Postal Service.

Thus, if mailing costs exceeded this year's $95.7 million appropriation by about $50 million, which Mathias' estimates indicated was probable, the Postal Service would have to absorb that amount.

To prevent that, the Senate imposed a seven-day moratorium on mass mailings so the Postal Service could determine how much of the $95.7 million is left for the rest of the fiscal year.

It also agreed to limit cost of mailings to half of what is left, reserving the other half of the unspent funds for the House, and to allocate the Senate share on the basis of state population.

According to the Postal Service, Congress had spent $69.5 million on official mail through May 21. That left $26.1 million available, of which slightly more than $13 million was the Senate's share. After reserving $654,151 for use by Senate committees and officers, $12.4 million remained to be divided among the 100 senators.

Under the old system, individual senators had no limit on what they could spend on mass mailings within the congressional appropriation for that purpose. Mathias compared the appropriation with a giant bowl of soup, around which the 100 senators and 435 House members stood, spoons in hand.

"Fellows who ladle the fastest will end up with the most soup," Mathias said. "Those who are not quick with the spoon will end up with the bottom of the bowl."

The new system, in effect only through the rest of this fiscal year, may be particularly painful to senators facing reelection bids in November and perhaps planning major mass mailings this summer before the onset of election-year restrictions on such activity.

According to figures compiled by the secretary of the Senate, seven of the top 12 Senate mailers -- all of whom were spending at annualized rates of more than $1 million -- face reelection contests this year.

Meanwhile, House members remain free to ladle away at Mathias' symbolic soup bowl to their hearts' content. The Senate resolution urged the House to impose a similar mailing restriction, but it could not bind the other chamber of Congress to do so.

Theoretically, the Senate reserved half of the remaining $26.1 million for the House, but in reality there is no limit on mailings by House members and no signs of enthusiasm for adopting the Senate's new system.