It is partly inflation and partly something else, but the same cost problems that eat away at everyman are chewing up the U.S. Senate's splendid new dream house.

And if senators were supersensitive and uncomfortable last year about the escalating cost of their new Philip A.Hart office building, this year some are bordering on the catatonic.

Last year, the estimated cost of the unfinished building was $135 million. This year, it is far higher - a "conversational" figure is $160 million - but no one knows how much higher.

Capitol Architect George M. White discussed, but that he is "sure" that the final cost will not be that high.

Alarmed by the developments, the Senate's building commission last week instructed White to produce a firm cost estimate and a list of pricecutting options.

"Until we get that new estimate, I don't want to talk about figures," said Sen. J. Bennett Johnston (D-La), chairman of the commission. "But the cost is definitely going to be more than the figure we talked about last year."

Johnston added, "The way we have been given these estimates has been a debacle. It has become a giant headached. We are criticized, the whole Congress is under fire for inflation, energy. This couldn't have come at a worse time."

Since 1973, when the earliest cost estimate was $47 million, the price tag has risen repeatedly - first to $68 million, then $72 million, then $85 million, then $122 million. Last year's $135 million was though to be final.

Ironically, one reason for the excalation is Congress itself. The House last year refused to go along with a Senate-approved appropriation of $54.8 million to finish the project.

The unusual House action - ordinarily, it does not interfere with Senate spending - came in the wake of criticism about the opulence of the Hart building at a time of budgetary constraints.

One result was that the Senate was unable to award contracts for interior finishing. A new budget request of $49 million, now pending in Congress, would allow continuation of that work.

The new delay, which has moved the completion schedule back another year to 1983, led Johnston and other members of the building commission to direct White to come up with a list of options for altering the last part of the project.

"The options could range from just letting it stay as it is, unfinished, to completing only alternating floors, to substituting less expensive interior finishing materials, such as using brick instead of marble, although I don't think anyone will want to do that," Johnston said.

Other options could include eliminating the senators-only rooftop restaurant, the gymnasium, the two-story hearing room with built-in television lights and broadcast booths for network anchormen.

Another commission member, Sen. Pete Domenici (R-N.M.), said, "It is an absolute disgrace, the way this has been handled. Either we get a firm figure or we are going to have to make some drastic changes."