Baltimore County Executive Donald P. Hutchinson has decided to abandon his longshot bid for the U.S. Senate seat, his friends and supporters said yesterday.

Hutchinson, the first Democrat to announce for the seat and, at 40, the youngest in the race, is scheduled to confirm his departure from the crowded field today in Towson, the county seat. Friends who spoke with Hutchinson yesterday said he gave little indication of what he would do next. "He's going to sit back and take the rest of the day off," said state Sen. Thomas L. Bromwell (D-Baltimore County). Hutchinson could not be reached.

Hutchinson cannot succeed himself after he completes his second term this fall as executive of the sprawling, conservative and largely Democratic Baltimore County.

Despite what many people considered a successful tenure as executive, an early campaign start last fall, and a fund-raising effort that was competitive with the other contenders, Hutchinson had made little headway in the Senate race.

According to most published polls, he consistently trailed front-runner Rep. Barbara Mikulski even in his home base of Baltimore County, despite his efforts to depict her as too liberal, despite the support of an array of elected officials from the state's more conservative rural wing, and despite a campaign that highlighted his administrative skills and purportedly moderate views.

Though some polls showed him running competitively with Gov. Harry Hughes and Rep. Michael Barnes, the other leading Democrats, in others he was a distant fourth. State Sen. John C. Coolahan (D-Baltimore County) said that a recent countywide poll taken by a local candidate merely confirmed the bad news. "He's spent money for the ads for the TV, but he just doesn't seem to be going anywhere," Coolahan said. "Rumor has it there's gloom around Towson."

During the weekend, political insiders speculated that Hutchinson would move to a campaign to oust one-term Republican Rep. Helen Bentley from her Baltimore County-based 2nd Congressional District seat. Recently, however, former assistant attorney general Kathleen Kennedy Townsend announced her candidacy for the Democratic nomination for the seat, and a key Hutchinson campaign aide, who asked to remain anonymous, ruled out a congressional bid.

Bromwell and other Baltimore County Democrats said yesterday that in a few short months of campaigning Townsend has made a favorable impression on many county Democrats and it would likely be perceived as unfair of Hutchinson to move into the race now.

In the past, Hutchinson also had made no secret of his desire to serve as the lieutenant governor candidate on a ticket headed by Baltimore Mayor William Donald Schaefer. But that option was ruled out by Schaefer's selection of Senate President Melvin Steinberg, also a Baltimore County Democrat.

As word of Hutchinson's decision spread yesterday, speculation immediately began over where his supporters would go. Mikulski supporters said that the departure would solidify the Baltimore region for her. Barnes' campaign manager Michael Cryor said, "I think that vote's going to be up for grabs . . . . " And Hughes aide and campaign manager Andrew Wigglesworth said that "clearly there are a lot of persons who will go to the governor because . . . the governor is a more moderate candidate."