Late yesterday afternoon, two Democratic congressmen from seaside states huddled in the speaker's lobby off the House floor, waiting for the right time to push for a vote on a bill to allow tax deductions for conventions held on cruise ships.

Their little bill was among 24 supposedly noncontroversial measures brought up under a suspension of House rules, and all they needed to pass it was an affirmative voice vote from two-thirds of the sleepy handful of colleagues on the floor.

"Come on, Frank, I think we've got an opening," said Fortney H. (Pete) Stark Jr. of California to Frank J. Guarini of New Jersey. "I don't see the guy anywhere." The "guy" was Rep. Donald J. Pease (D-Ohio), who had made it known that he thought the cruise ship bill was a ripoff and that he would move to torpedo it when Stark and Guarini pressed for passage.

With Pease out of sight, Stark moved swiftly to the floor to seek recognition for the bill. His support of it, he confessed, was "hardly a profile in courage." But the American cruise ship industry needed it to keep up with foreign competitors, he said, and besides the tax laws were inequitable now because cruise ships were just floating hotels, and hotel conventions were tax deductible.

Stark looked confident when the bill came up for a vote, since Pease was still not around and nobody else in the chamber seemed to be paying any attention. But at the last minute, up popped Rep. Millicent Fenwick (R-N.J.), demanding that the bill be subjected to a roll call of the full House.

"I'd like to know who put her up to it," said Stark somewhat wistfully after his strategy was foiled.

"Oh, my dear. Anyone could see that was an awful bill," said Fenwick. "Junkets here, junkets there. I couldn't find Mr. P. so I got up myself. He rushed over to me afterward and said, 'Thank God you were there, Millicent.' Tax deductible cruises, of all things!"

The bill fell short of the needed two-thirds; the vote was 219 to 164.

During Senate Finance Committee debate last week on the nickel-a-gallon increase in the gasoline tax, the subject was whether to exempt gasohol, which grain-state committee Chairman Robert J. Dole (R-Kan.) plainly thought was a good idea.

Sen. Bill Bradley (D-N.J.), from a state with a keen interest in passage of the bill's mass-transit funding provisions, wondered how much the gasohol exemption would cost.

"About as much as you'd get if you knocked out mass transit," Dole replied crisply.

"The issue has suddenly come into focus," Bradley said.

The gasohol exemption was then agreed to without a vote. The Treasury estimates it would cost about $1 billion over the five-year life of the bill; the bill includes about $1 billion a year in new money for transit.

Being a lame duck, Sen. Harrison H. Schmitt (R-N.M.) doesn't have much time left to do all the good things a senator is supposed to do. But with a little help from colleagues, he was able last week to check one more item off his shopping list before Christmas.

House conferees agreed to add a tidy $169,000 to the more than $30 billion agriculture appropriations bill for fiscal 1983. They acted after Sen. Thad Cochran (R-Miss.), conference chairman, warned that a "disturbed" Schmitt would "really cause trouble" otherwise.

The extra money will allow vital research to continue on . . . the range caterpillar.

But another lame duck, Rep. Don H. Clausen (R-Calif.), isn't having such good luck. He can't get a little farewell project of his off the dime.

Just before the election recess, Clausen persuaded the House to exempt Louisiana Pacific and Crown Simpson, operators of two big pulp mills in his district, from certain ocean discharge requirements of the federal water pollution control law. It was to be a one-time-only exemption, Clausen's bill said.

The measure passed with support of the companies, the state of California and some environmentalists. But the federal Environmental Protection Agency opposes it and the bill, despite Clausen's best efforts, is mired in the Senate, with little chance of seeing light of day.